What Is SEO and How Does It Actually Work?

SEO, or search engine optimisation, is the practice of shaping a website so that search engines can find it, understand what it's about, and confidently show it to people searching for related things — without paying for the placement. Every technique that falls under the SEO umbrella, from page speed to backlinks, exists to influence one of those three steps: discovery, understanding, or trust.

The Three Jobs a Search Engine Has to Do

Before ranking anything, a search engine has to crawl the web to find pages, index what it finds so it can be retrieved instantly later, and then rank the indexed pages against each other for a specific query. Most SEO problems trace back to a failure at one of these three stages — a page that isn't ranking might not even be indexed yet, and a page that isn't indexed might never have been discovered by a crawler in the first place.

Crawling: How Search Engines Find Your Pages

Search engines discover new pages by following links — from other sites, from your own internal navigation, and from your XML sitemap. A page with no links pointing to it from anywhere is effectively invisible, no matter how good the content is. This is exactly why internal linking isn't just a nice-to-have; it's often the only path a crawler has to reach your deeper pages at all.

Crawl budget — how much of a site a search engine is willing to crawl in a given period — becomes a real constraint on larger sites. I've seen this go wrong most often on ecommerce catalogues, where faceted navigation generates so many filter URL variants that crawlers spend their entire budget on pages that will never rank, instead of the product pages that actually matter.

Indexing: Getting Onto the Shortlist

Once a page is crawled, the search engine decides whether to add it to the index — the enormous database it actually searches through to answer queries. Pages get excluded from the index for reasons that have nothing to do with quality: a stray `noindex` tag left over from staging, a canonical tag pointing somewhere else, or duplicate content that's technically identical to a page already indexed. Checking Search Console's coverage report for excluded pages is usually the fastest way to catch this before it costs months of visibility.

Ranking: Why Some Pages Beat Others

Ranking is where the hundreds of individual signals come in, but almost all of them fall into a handful of categories: relevance to the query, page experience (loading speed, mobile usability, stability), content quality and depth, and authority signals like backlinks and brand mentions. None of these work in isolation — a fast page with thin content won't outrank a slower page that actually answers the question better, and the reverse is just as true.

• Relevance — does the page's content and structure genuinely match search intent, not just the keyword
• Page experience — covered in detail in my Core Web Vitals checklist
• Content depth — does the page answer the question completely, or just gesture at it
• Authority — do other trusted sites, and your own site's internal structure, vouch for this page

Technical SEO vs On-Page SEO vs Off-Page SEO

These three categories cover almost everything in the field, and confusing them is the most common reason SEO efforts stall. Technical SEO is the plumbing — crawlability, indexability, site speed, structured data — and it's a prerequisite, not a growth lever on its own. On-page SEO is the content and HTML of the page itself: headings, keyword targeting, internal links, and how clearly the page answers the query. Off-page SEO covers everything that happens elsewhere but still signals trust back to your site, primarily backlinks and brand mentions.

A site with perfect technical SEO and no content depth won't outrank a competitor with genuinely useful content, and a site with brilliant content buried behind slow load times and broken indexing will never get the chance to prove it. All three layers have to work together.

Local SEO and Ecommerce SEO Are the Same Rules, Applied Differently

Local SEO and ecommerce SEO aren't separate disciplines with their own rules — they're the same crawling, indexing, and ranking mechanics, applied to a specific context. For a local business, the Google Business Profile becomes a major additional ranking surface, which is why category precision and service area accuracy matter so much. For an online store, the sheer number of product and filter URLs makes crawl efficiency the dominant technical concern, which is what WooCommerce SEO at scale is really about.

How AI Search Changes the Picture

AI-powered search and answer engines still rely on the same underlying crawl-index-rank mechanics, but they add an extraction step on top: after finding a relevant page, the system has to pull out a specific, citable answer. This rewards clear entity naming and answer-first writing even more than traditional search did — a topic I go into in depth in Structuring Content So AI Search Engines Can Actually Use It.

Why SEO Takes Time

Search engines re-crawl and re-evaluate pages on their own schedule, not yours, and ranking signals accumulate rather than switching on instantly. This is also why migrations are so risky — moving a site resets a lot of that accumulated trust unless it's handled carefully, which is exactly what my migration checklist is designed to prevent. Realistic timelines for meaningful movement are usually measured in weeks to a few months, not days.

Where to Start

If you're new to SEO, start by confirming your site is actually crawlable and indexed correctly — that's the foundation everything else sits on. From there, work outward through page experience, content depth, and finally authority building. SEO is also just one channel among several — if you're weighing it against paid ads, social, or a full agency retainer, my guide to choosing a digital marketing agency breaks down how the channels compare by business stage. If you'd rather skip the diagnosis and have someone map out exactly where your site stands, get in touch with your URL and I'll tell you which of these three jobs — crawling, indexing, or ranking — is actually holding you back.