Search engine optimisation (SEO)

What is a search engine and how do they work?


Understanding how search engines work can help your business use SEO to reach potential customers.

What is a search engine?

Search engines allow users to search the internet for content using keywords. Although the market is dominated by a few, there are many search engines that people can use. When a user enters a query into a search engine, a search engine results page (SERP) is returned, ranking the found pages in order of their relevance. How this ranking is done differs across search engines.

Search engines often change their algorithms (the programs that rank the results) to improve user experience. They aim to understand how users search and give them the best answer to their query. This means giving priority to the highest quality and most relevant pages.

How do search engines work?

There are three key steps to how most search engines work:


Search engines use programs, called spiders, bots or crawlers, to scour the internet. They may do this every few days, so it is possible for content to be out-of-date until they crawl your website again. 


The search engine will try to understand and categorise the content on a web page through 'keywords'. Following SEO best practice will help the search engine understand your content so you can rank for the right search queries. 


Search results are ranked based on a number of factors. These may include keyword density, speed and links. The search engine's aim is to provide the user with the most relevant result. 

Although most search engines will provide tips on how to improve your page ranking, the exact algorithms used are well guarded and change frequently to avoid misuse. But by following search engine optimisation (SEO) best practice you can ensure that:

  • Search engines can easily crawl your website. You can also prompt them to crawl new content.
  • Your content is indexed for the right keywords so it can appear for relevant searches.
  • Your content can rank highly on the SERP. 

Directory search engines

Some niche search engines operate as directories for specific types of content. This mean that they only show results for content that is manually added. They do not crawl the internet. SEO tactics can still be used to rank highly for relevant queries within these directory search engines.

Rich media search results

Universal or 'blended' search is how search engines present different content types in the search results to users. As well as the traditional text page results, the SERP will also show rich media content, such as images, videos, maps, articles and shopping pages.

Having several different types of content on your website - for example, an instructional video on how to use your product, or a blog - could impact on your chances of appearing on results pages and how highly you are ranked. 

You can use 'structured data' on your website to help search engines understand and display specific types of content. This is a code added to the HTML markup. Using structured data means that information such as review ratings, images, addresses and phone numbers can appear on the search engine results page.