What Is Search Engine Optimisation and How Does It Work?

Type a question into Google and results arrive in under a second. Behind that speed sits a system that crawls billions of pages, stores them in an index and ranks them by how well each one answers the question.

Search engine optimisation, or SEO, is the practice of helping your pages perform well in that system. It earns organic visibility, which means unpaid positions in search results.

The three stages of search

Search engines work in three stages.

Crawling: automated programmes follow links across the web and discover pages.

Indexing: the search engine reads each page, works out its topic and stores it in a vast database.

Ranking: when someone searches, the engine selects indexed pages that match the query and orders them by relevance, quality and usefulness.

SEO influences each stage. A page that cannot be crawled will never be indexed, and a page that is never indexed will never rank.

The four areas of SEO

Technical SEO makes your site easy to crawl and fast to load. It covers site architecture, mobile performance, structured data, HTTPS and clean code.

On-page SEO shapes the content of each page. Titles, headings, copy and internal links tell search engines and readers what the page covers.

Content SEO builds pages that answer real questions in depth. Strong content matches what a searcher wants, whether that is a definition, a comparison or a product.

Off-page SEO builds authority. Links and mentions from trusted websites signal that others value your content.

Search intent

Every search carries an intent. Some searchers want to learn, some want to compare options and some want to buy. A page ranks well when its content matches the intent behind the query.

Review the results already ranking for a phrase and you will see what Google believes searchers want. A page of guides, a list of products or a comparison table each tell you which format to build.

Why SEO matters

Search often starts the journey. People look for answers, suppliers, products and local services, and a business that appears early earns attention at the moment of need.

SEO also compounds. A well-built page continues to attract visitors long after you publish it, so each piece of work adds to a growing base of organic traffic.

SEO and AI search

AI tools such as ChatGPT, Perplexity, Claude and Gemini now answer many questions directly. They draw on the same web content that search engines index. Pages with clear structure, strong authority and accurate information tend to perform well in both places, so a sound SEO foundation supports visibility in AI answers too.

How long SEO takes

SEO builds over months. Early weeks cover audits, fixes and planning. Content and authority work follows, and rankings improve as search engines recognise the value of your pages. Track progress in rankings, organic traffic and, most importantly, the enquiries and sales that organic search delivers.

Where to begin

Start with an audit. It shows how search engines currently see your site, which technical issues hold it back and which pages already earn visibility. A clear picture of today’s position gives every later decision a firm foundation.