What is SEO? A complete guide to search engine optimization

Search engine optimization (SEO) is essentially how you make your brand visible to the people searching for what you offer. 

This guide covers what SEO is, how it works, and how to start doing it yourself. Including what’s changed about SEO over time.

SEO is about visibility, not rankings

SEO is no longer about earning a position for a specific keyword. It’s about your full search visibility: how often and how prominently you show up across search results that change with every user and every search platform.

The old SEO model was simple. You picked a keyword, optimized content around it, climbed to a high position in search engine results, and tried to hold that position. 

The new SEO model is more complex. The results searchers see are now more personalized, varying by who’s searching, where they’re searching, what device they’re using, and which platform they’re searching on. 

And just because you show up on the first page of Google’s organic results, doesn’t mean you’ll show up in the AI Overview or be picked up by ChatGPT. 

Our AI Mode study found that AI Overviews pulled from the top 10 Google URLs only about two-thirds (67%) of the time. The overlap between AI Mode and the top 10 Google results was 35%. And lower still when comparing ChatGPT and Google’s top 10 results.

Ranking well is still helpful. The same Semrush study found that domains in Google’s top 10 results are far more likely to get cited by AI. But a number 1 position no longer guarantees a click, a citation, or even a steady place in the results. 

You’re not optimizing for a single position anymore. You’re building visibility that holds up across every surface and every searcher.

What is SEO?

SEO stands for search engine optimization, and it’s the process of making your website more visible in search engines like Google and AI systems like ChatGPT without paying for ads. 

Put simply, SEO is about getting found when someone searches for what you offer.

The goal of SEO is organic (unpaid) visibility. This could mean showing up more prominently in  search engine results pages (SERPs) or getting cited inside an AI-generated answer. 

Whether a search engine or an AI system decides to show your page generally comes down to three things:

• Relevance: How well your content matches what the searcher actually wants
• Authority: How trustworthy you appear to be
• Structure: How easily a machine can find, read, and parse your site

Why is SEO important?

SEO is important because it helps you build sustained visibility that translates to better business results.

And while AI chatbots are shaking up the search environment, SEO is as relevant as ever. It’s just changing — and there’s evidence to back it up:

• Google says people search more often in the AI era. Google also reports that AI Overviews drove over 10% growth in the query types where they appear in major markets like the U.S. and India.
• Semrush research found that AI search visitors are worth ~4.4x more than organic search visitors based on conversion, likely because they arrive further along in their decision by the time they click

Read together, those numbers say visibility is moving to more surfaces, and the brands that adapt their SEO techniques to the new surfaces are the ones capturing demand.

How is SEO different from paid search?

SEO earns visibility organically, while paid search (also called PPC) buys visibility. 

With SEO, you optimize your content and online presence. With paid search, you bid on terms to show ads above or alongside the organic results and pay each time someone clicks.

The trade-off is speed versus staying power. Here’s how SEO and paid search compare:

	SEO	Paid search (PPC)
Cost	You don’t pay anything beyond what it costs to create and maintain your content and online presence	You pay for every click in addition to what it cost to create the ads
Time to results	Weeks to months	Almost immediate
Longevity	Compounds and keeps working without much additional time or investment	Ends the moment you stop paying
Trust among searchers	Tends to be seen as more trustworthy	Seen as less trustworthy since users know it’s paid
Best for	Long-term growth, brand authority, and evergreen or research-stage topics	Product launches, promotions, testing offers, and high-intent keywords

It’s worth noting that ads are starting to appear inside AI experiences, too. 

Google has been rolling out ads in AI Overviews and testing them in AI Mode. And other AI platforms are exploring sponsored placements. So, the paid-versus-unpaid split is following users onto AI surfaces. 

What are the three main types of SEO?

The three main types of SEO are on-page SEO, technical SEO, and off-page SEO. 

According to Zach Paruch, AI Visibility & SEO Strategist at Semrush:

“On-page SEO is fundamental to how/whether AI search tools understand when your content is relevant to a question. Technical SEO makes that content easy to find and use. Off-page SEO shapes what your brand is known for and how it’s perceived through relevant backlinks, reviews, positioning, and third-party mentions.

Together, these three types of SEO increase the likelihood that your brand is mentioned, accurately described, and recommended in AI search answers.”

1. On-page SEO

On-page SEO is the work you do on your own webpages to make them relevant, useful, and easy to understand. It covers everything on the page itself, including:

• Creating helpful, in-depth content that satisfies the searcher’s intent
• Adding internal links to related pages and external links to credible sources
• Writing descriptive alt text for your images
• Structuring the page with clear headings, so both readers and machines can follow it
• Working your target keywords naturally into the body content, title tag, headings, URL, etc.

Here’s an example of how we incorporate keywords into content on the Semrush blog:

2. Technical SEO

Technical SEO involves improving your site from a technical standpoint, which is largely about ensuring your site is easy to crawl and index. 

Common technical SEO tasks include ensuring a logical site architecture, prioritizing page speed, using a mobile-friendly design, and maintaining a sitemap that lists your most important pages.

The focus on crawlability is for good reason: A bot has to be able to crawl your site before you can be shown in search results. That’s true for appearing in both Google and AI platforms.

3. Off-page SEO

Off-page SEO is everything you do beyond your own site to build visibility, mostly by earning backlinks and mentions from other credible sources. 

When trusted sites point to your content or mention your brand, search systems see you as more trustworthy. 

A recent Semrush study shows that the sources AI tools cite most are community and reference platforms like Reddit, LinkedIn, YouTube, and Wikipedia.

How do search systems work?

Search systems work by discovering content, organizing it, and deciding what to show in response to a query. 

Let’s go over both search engines and AI platforms in more detail:

How do search engines work?

Search engines work by crawling, indexing, and ranking content from across the web. 

Here’s what each step involves, assuming everything goes perfectly:

• Crawling: Automated bots (also called crawlers or spiders) discover content around the web, primarily by following links 
• Indexing: The search engine analyzes each page it finds and, if the page qualifies, stores it in a huge database of possible results
• Ranking: When a user performs a search, the search engine interprets their search intent and uses a complex algorithm to present the best and most relevant results from the index

Search engines use many ranking factors. Some of the most important are the relevance and quality of your content, the number and quality of links pointing to it, and your site’s usability.

In addition to the ranked organic links, search engines also show SERP features like featured snippets, image packs, and AI Overviews. Those features can change how much attention the standard links get.

How does AI search work?

AI platforms work by interpreting your question, retrieving relevant information from across the web, and synthesizing it into a single answer — often with citations. 

Unlike search engines, AI platforms don’t hand you a list of links to sort through. They source information and write the response for you. 

It happens in roughly four steps:

1. Query interpretation: A large language model (LLM) reads your question to work out the intent and context
2. Query fan-out: The system often breaks one question into several sub-queries to cover more angles. The query “best tent for family camping during fall” might break down into many sub-queries covering capacity, weather resistance, and price that the model runs searches for.
3. Semantic retrieval: Rather than matching your exact keywords, the system matches by meaning. It interprets what you’re really asking and pulls the passages that answer it, even when they use different words.
4. Synthesis and citation: The model composes a natural-language answer based on passages retrieved and cites the most relevant sources

How to get started with SEO: 5 core practices

To start with SEO, work through five core practices: keyword research, content creation, on-page optimization, technical health, and earning links and mentions. 

Research keywords and prompts

Do keyword research to find out what your audience is searching, so you can create content that matches real queries.

One way to find keywords is with Semrush’s Keyword Magic Tool. Enter a broad term related to your business, add your domain, choose your country, and click “Search.”

You’ll see a Personal Keyword Difficulty (PKD) score next to each keyword. For beginners, look for keywords with a PKD between 0 and 29 to find terms you can realistically appear for.

You can also use these keyword metrics to identify the best keyword opportunities:

• Intent: The type of search intent behind the keyword, meaning what the user wants to achieve. It can be informational, navigational, commercial, or transactional.
• Volume: The keyword search volume, which is the average number of monthly Google searches, according to our data
• SF: The number of types of SERP features present. Click the number to see which ones they are and get insight into search intent. Or click the icon to see the SERP for yourself.

After you finish finding keywords, move on to prompts — the longer, conversational queries people ask tools like ChatGPT, Perplexity, and Google’s AI Mode.

To find them, use Semrush’s Prompt Research tool. Enter your topic or and click “Analyze.” It will uncover potential prompts relevant to you that users ask AI tools, along with the AI’s response and which brands get mentioned for each one. 

This gives you an idea of the kinds of content you need to create to be cited and recommended by AI.

Create quality content

Creating quality content that genuinely helps the user is likely to perform well in search. 

Start by matching the format to the searcher’s intent for the topic you’re covering (e.g., someone searching “best tent” wants tested recommendations — not an overview on the history of camping). Then, aim to cover the topic better than the pages already ranking.

The framework Google’s quality raters use to judge content isExperience, Expertise, Authoritativeness, and Trustworthiness (E-E-A-T). It isn’t a direct ranking factor, but it’s helpful to treat this as a guide on what strong content should look like.

Here’s a more detailed breakdown of E-E-A-T:

• Experience: First-hand involvement with the topic. Have you actually used the product you’re reviewing, visited the place you’re talking about, or done the workflow you’re sharing?
• Expertise: Real knowledge or skill in a given area, which can be backed by credentials or a track record
• Authoritativeness: Recognition as a go-to source that others reference and link to
• Trustworthiness: Whether readers can rely on your content to be accurate and honest. It comes from things like getting the facts right, citing credible sources, and running a secure site. Google considers this the most important of the four.

As generic, AI-generated filler becomes more common, the way to stand out is to publish what a model can’t manufacture. That means leaning on first-hand experience, original data, real examples, expert quotes, and a genuine point of view. 

Plus, many of the same originality and authority elements that make your content stand out to a reader are what make AI systems mention and cite it.

Optimize on-page elements

Optimizing on-page elements helps search engines and AI understand what your page is about and who it’s for. 

And because on-page elements are fully in your control, those optimizations are some of the easiest SEO work you can do. 

The most important on-page elements are the:

• Title tag: An HTML element that provides a webpage title that can show up in places like SERPs, link previews, browser tabs, and AI responses
• Meta description: An HTML webpage description that may show in search results
• H1 and subheadings: Your on-page title and section headers
• URL slug: The last part of a URL address that serves as the page’s unique identifier 
• Alt text: An HTML image description that tells search systems and screen readers what’s being shown

Work your keyword into the above places naturally, plus throughout the body copy. Don’t force it — keyword stuffing reads badly and is unlikely to show prominently in search.

To easily check for issues with your on-page SEO, use Site Audit. Once it crawls your domain, the “Issues” report flags on-page problems like missing or duplicate title tags and meta descriptions, missing H1s, and images without alt text that you can fix.

Maintain technical health

Maintaining your website’s technical health ensures search engines and AI crawlers can access and display your content in search results.

Start with a technical SEO audit. Enter your domain into Semrush’s Site Audit tool, follow the prompts if you haven’t yet run a crawl, and go to the “Overview” tab. Click the number in the “Errors” section to see the most critical issues first.

For any issue, click “How to fix” to learn more about what’s wrong and how to resolve it. Use the “Share” button to work on the project with co-workers. 

Address errors first, then warnings, then notices.

Earn links and brand mentions

Earning high-quality backlinks and brand mentions tells both search engines and AI systems that you’re credible.

Backlinks are the foundation of improving your authority for SEO, and they’re also important for AI search. Know that a few links from relevant, trusted domains do more for improving your authority than dozens of low-value ones.

Brand mentions matter as well, even the ones without links. When respected publications and communities talk about your brand, it builds a reputation that makes search systems more likely to trust and cite you. 

To gain relevant backlinks, use Semrush’s Link Building Tool. It surfaces prospects based on your specified keywords, your domain, and your competitors’ domains.

Move the prospects you want to contact to the “In Progress” tab by clicking the “To In Progress” button, send outreach right from the tool, and monitor the backlinks you acquire over time. 

To grow mentions, show up where your audience already looks. Contribute genuinely on platforms like Reddit, LinkedIn, and YouTube (with helpful answers, not spam), pitch yourself as an expert source for journalists, and publish original data or research worth referencing. 

How to measure SEO success

Measure your SEO success by tracking organic search and AI visibility metrics, then adjusting based on what the numbers tell you. 

Start with the core SEO metrics:

• Rankings: Where your pages appear in search results for target keywords
• Organic traffic: The visits organic search brings to your site
• Impressions: How often you appear in search results
• Click-through rate (CTR): The share of how many impressions turn into clicks
• Conversions: The number of desired actions users complete

Google Search Console (GSC) shows impressions, clicks, CTR, and average position. Google Analytics 4 (GA4) tracks organic traffic and conversions. 

To keep tabs on the keywords that matter most to your business, set up Semrush’s Position Tracking tool. Add your domain and keywords to see daily position changes, plus whether you’re appearing in SERP features like featured snippets and AI Overviews.

Next, track the metrics that measure AI visibility and impact:

• AI citations: How often AI platforms cite or link to your content as a source
• AI mentions: How often your brand appears in AI answers 
• AI mention prominence: How high up in the AI answer you appear
• Sentiment: How positively AI platforms describe your brand. It can be positive, neutral, or negative.
• AI referral traffic: The visits AI platforms actually send to your site.

GSC features a dedicated Generative AI performance report designed to track how your site performs in AI experiences like AI Mode and AI Overviews. And GA4 has an AI assistant channel for referral tracking.

To track your AI visibility metrics across AI platforms, use Semrush’s AI Visibility Toolkit. You can see the prompts you and your competitors appear in, find topic opportunities, and get personalized suggestions on how to improve your AI visibility.

Keep in mind that AI results are a lot more volatile than Google rankings. Overall visibility beats chasing individual placements. SEO and AI Visibility Consultant Bill Widmer, who runs a weekly tracker of which URLs AI engines cite, puts it this way:

“The biggest lesson from tracking AI citations every week is how unstable any single one is. The same page gets cited across ChatGPT and Perplexity one week and vanishes the next, and the answer changes from one user and one conversation to the next. What actually moves the needle is your overall presence.”

For teams managing AI visibility across many brands, markets, or languages, Enterprise AIO allows for tracking at scale and ties it to traffic and conversion data.

How to learn SEO in 2026

The best way to learn SEO in 2026 is to practice it and continue your education using free resources.

Begin with the free courses at Semrush Academy. Pair the courses with hands-on work to amplify your learning. Start by running an audit, publishing something, and watching what moves in your metrics.

Then, see exactly where your brand shows up across AI answers with Semrush’s AI Visibility Toolkit.