How does SEO work? How Google finds, understands and ranks your pages

Short answer: SEO works by making it easy for Google to do three things with your website. First find your pages, then understand and store them in its index, and finally judge that your page is the best answer to a search. All SEO work, from technical fixes to content and links, affects one of those three steps.

If you are completely new to the topic, start with What is SEO? This article goes a step deeper into the machinery. Google handles about 91 percent of searches in the UK and Bing about 6 percent (StatCounter), so we focus on Google, but the principles are the same for other search engines.

Google's three steps

Google itself describes its search engine in three stages: crawling, indexing and serving search results (Google Search Central). Not every page makes it through all three.

Step 1: crawling

Google uses automated programs, called crawlers or robots, that download text, images and video from the web. Its robot is called Googlebot. It finds new URLs in two ways: through links from pages it already knows, and through sitemaps that site owners submit. Google also runs a page's JavaScript in a current version of Chrome to see the page as a visitor would (Google Search Central).

What SEO does at this step:

• Links pages internally so none becomes a dead end.
• Submits a sitemap in Google Search Console.
• Checks that robots.txt does not block important pages.
• Fixes broken links, long redirect chains and server errors.

Bing and several other search engines also support IndexNow, a way to tell them directly that a page has changed (IndexNow). Google does not take part. We describe the technical work in more detail on our technical SEO page.

Step 2: indexing

Once a page is fetched, Google tries to understand what it is about. It analyses the text, headings, images and code, works out whether the page duplicates another, and if so chooses the most representative version, the canonical (Google Search Central).

The result is stored in Google's index. It contains hundreds of billions of web pages and is more than 100 million gigabytes in size. Google compares it to the index at the back of a book (Google).

Two things many people do not know: indexing is not guaranteed, and not every page Google fetches is stored (Google Search Central). Google also says it is not a goal to have 100 percent of your pages indexed (Google Search Console Help). Read Google indexing for how to check and fix it.

What SEO does at this step: writes clear headings and page titles, avoids several near-identical pages, sets the right canonical URL and makes sure the important things are in the text, not only in images.

Step 3: ranking

When someone searches, Google looks for matching pages in the index and sorts them. Google does not accept payment to rank pages higher, and ranking is done by software (Google Search Central). Google describes five main factors (Google):

1. Meaning of the query. Language models work out what the searcher really means, even with typos or everyday language.
2. Relevance. The most basic signal is that the page contains the same words as the search. Then Google looks at whether the content actually answers the question.
3. Quality. Signals of expertise, authority and trustworthiness, for example whether well-known sites link to the content.
4. Usability. When everything else is equal, pages that work well on mobile and load fast win.
5. Context. Location, search history and settings. A search for "plumber" gives different results in Bristol and Glasgow.

The quality part is often summed up as E-E-A-T: experience, expertise, authoritativeness and trustworthiness, with trust weighing most. Google says E-E-A-T is not a single ranking factor, but something several signals together try to capture (Google Search Central). Google's quality raters judge results using guidelines last updated in September 2025, but their ratings are not used directly in ranking (Google).

The systems behind ranking

Behind those factors sit a number of automated systems that Google lists openly (Google Search Central). Some of the most important:

• BERT, MUM and neural matching understand the language in queries and pages.
• Link analysis and PageRank interpret how pages link to each other.
• Freshness systems show newer content when it matters.
• The reviews system rewards in-depth reviews and tests.
• Passage ranking can find a good answer in a single paragraph on a long page.
• Spam detection filters out pages that break Google's rules.

The former helpful content system has been part of Google's core systems since March 2024. Page experience has its own explanation: Core Web Vitals are used by the ranking systems, but there is no single signal and good scores do not guarantee a top spot (Google Search Central). Read Core Web Vitals explained.

The systems change all the time. In 2023, Google ran more than 700,000 experiments that led to 4,781 changes to Search (Google). That is why SEO is ongoing work, not a one-off project. Read How long does SEO take?

An example from start to finish

Say an accountancy firm in Leeds publishes a new page about year-end accounts for limited companies.

1. Crawling. The page is linked from the homepage and services menu and is in the sitemap. Googlebot finds it quickly.
2. Indexing. The page title, heading and text clearly cover year-end accounts in Leeds. There is no near-identical page on the site. Google stores it.
3. Ranking. When someone in Leeds searches "year end accounts limited company", the page is compared with competitors. It answers clearly what is included and what it costs, loads fast on mobile, the firm has good reviews and a local paper has written about it. The page ranks high.

If one step is missing, for example the page is never linked or the text is thin, the rest matters less. If you want to see where your own site gets stuck, an SEO audit is a good first step.

Where AI search fits in

Google's AI Overviews and AI Mode are built on the same index. There are no extra requirements to appear there, but the page must be indexed and eligible to show with a snippet (Google Search Central). Traffic from AI features appears in Search Console together with ordinary web traffic. The same groundwork applies. Read more in Google AI Overviews.

Four common misunderstandings

• "You can pay Google for a better ranking." No. Ads are labelled and separate from the organic results.
• "More keywords in the text give a higher ranking." Relevance starts with the right words, but Google judges whether the page answers the question, not how often the word is repeated.
• "A fast site is enough." Speed helps when everything else is equal, but it does not replace good content.
• "SEO is done once the site launches." Competitors, search habits and Google's systems change all the time.

To follow how your own site is doing, start by verifying it in Google Search Console, making sure Google can reach your pages and submitting a sitemap (Google Search Central).