Search engines such as Google and Bing crawl billions of pages in order to discover and organise the content that appears on Search Engine Results Pages (SERPs). They exist to understand content in order to give users on their SERP the most relevant results to answer the questions that users are asking. Understanding how search engines work is crucial for SEO because if your website cannot be found, then it will not appear on the SERP, and users will not be able to find your website.
Customers are increasingly searching online for products and services, and it is now more common for users to access a website via a search engine rather than typing a web address directly. It is therefore important to rank highly on the search engine results pages, and to do that, it helps to understand how search engines work so you can optimise your site and attract more organic traffic.
What Are Search Engines?
A search engine is a software system that allows users to find information based on keywords or phrases. These systems return results extremely quickly by (1) crawling websites, (2) indexing their content, and (3) ranking them. The goal is to show the most relevant and useful pages for a user’s query.
One of the most dominant search engines is Google, and it uses a highly complex algorithm (composed of hundreds of factors) to decide which pages to show for which queries. Google makes thousands of changes to these algorithms each year (many unannounced), and periodically rolls out major updates that can shift rankings significantly.
In recent years, Google has also leaned into AI-driven enhancements (for example, using models to better understand context, synonyms and user intent) and more advanced signals such as multimodal indexing (understanding images, video and even audio). These trends are likely to become more important over time.
How Do Search Engines Work?
Search engines generally follow three main stages: crawling, indexing, and ranking. Not all pages make it through all three.
1. Crawling
Crawling is the process of discovering pages on the web. Google and other search engines deploy automated “spiders” or bots to fetch web pages, including their text, images and embedded media. Because there’s no master register of every web page, search engines must constantly explore the web, following links from known pages, and also discovering pages via submitted sitemaps or URL submission tools.
They revisit pages periodically to check for updates. Frequently updated or high-authority pages tend to be crawled more often.
2. Indexing
Once crawled, a page is analysed to understand what it’s about: the text, images, videos, metadata, structured data, etc. This information is stored in the search engine’s index, a huge, distributed database of content.
In modern indexing, search engines try to understand entities, relationships and semantics, not just keywords. They look at content freshness, page layout, metadata, internal linking structure, and user engagement signals (e.g. dwell time, click behaviour) to decide how to represent the page in their index.
Search engines do not index every fetched URL. Reasons a page might not be indexed include:
- A noindex directive (in a meta tag or via HTTP header)
- The page is considered low value (thin content, duplication, or boilerplate)
- The page returns an error (404, 500, etc.)
If your page is indexed, it becomes eligible to appear in search results, provided it meets other ranking criteria.
3. Ranking
When a user searches for a keyword on Google, Google will look through their index for content that is relevant to that keyword in the hope that it will answer the user’s query. They will rank the content with the content that they think is the most relevant at the top, so it is likely that the higher a website ranks, the more relevant Google thinks that website is in relation to the keyword/ query.
This is where Google’s algorithms come into play. Search algorithms are systems that are used to rank data from the search index and deliver the most relevant web pages for a query. Google uses many ranking factors in its algorithms to ensure the most relevant web pages will rank highest on the SERPs, including (but not limited to):
- Backlinks / authority: Inbound links from reputable, topically relevant sites still carry weight
- Relevance / content quality: How well the content aligns with the query’s intent, depth, clarity, and usefulness
- User experience / page performance: Page speed, Core Web Vitals, mobile friendliness, interactivity, layout stability
- Content freshness / updates: Recent updates can give a boost for queries where freshness matters
- Structured data / rich snippets: Use of schema markup (for e.g. FAQs, product info, reviews) helps search engines understand and present your content more attractively
- User engagement signals (indirect): Click-through rate (CTR), bounce/dwell time, pogo sticking
- Personalisation / searcher context: Location, device, previous search history, language settings
- Multimodal signals: For pages with images, video, audio – those media assets are increasingly considered (with better image & video understanding)
Over time, Google (and other engines) also increasingly rely on AI / machine learning to interpret context, surface helpful “featured snippets,” and surface content in more conversational / generative fashion (e.g. “search generative experience”). Keeping content structure, clarity and authority strong is more important than ever in that environment.
How To Make Your Website Search-Engine Friendly
Here are actionable points to ensure your site is crawlable, indexable, and competitive in today’s search landscape:
- Create and submit a sitemap / index management. Use XML sitemaps (and optionally JSON-LD index cues) to help crawlers discover your pages
- Ensure indexability. Avoid noindex blocking of important pages; fix errors and redirect chains
- Keyword & topic targeting. Use keyword research tools (e.g. Ahrefs, Semrush, or newer AI-driven tools) to find what your audience actually searches
- Write high-quality, helpful content. Focus on comprehensive, well-structured content that satisfies user intent
- Use internal & external linking strategy. Help search engines navigate and understand your content structure; link to trusted external sources
- Optimise for performance & user experience. Prioritise fast loading, smooth UX, good Core Web Vitals metrics, accessibility, and mobile friendliness
- Implement structured data / schema markup. Use relevant schema (e.g. FAQ, product, review) to help search engines interpret and enhance your listing
- Update content regularly. Refresh existing pages, remove outdated info, and show that your content is current
- Earn authoritativeness / backlinks. Continue to build quality backlinks from relevant domains (quality > quantity)
- Monitor and adapt to algorithm changes. Watch industry updates, test changes, and lose fear of refining your SEO
- Use multimedia where relevant. Incorporate supporting media (images, video, charts) with proper alt text, captions, and structured data
- Leverage AI & generative content wisely. Use AI tools to assist ideation or drafting, but always human-check, refine, and add value
Search engines exist to provide users with the most relevant and useful results. They crawl the web, index content, and rank pages based on a mix of signals. As search technology evolves, especially under the influence of AI and better media understanding, the fundamentals of clear content, strong UX, and authority remain core to effective SEO. By optimising your site to be crawlable, indexable, and competitive, you help ensure it can be discovered and valued by both users and search engines, driving organic growth over time.