How search engines work, from the crawl to the AI answer.

What is a search engine?

A search engine is a system that collects pages from across the web, stores them in a huge index and, when you type a question, picks and orders the pages most likely to answer it. Google, Bing, Yahoo and DuckDuckGo all do this, matching each search with the most useful result in a fraction of a second.

Search engines do not search the live web when you press enter. They search their own copy of it, built in advance. That is the key idea behind everything else on this page, and the reason a brand-new page can take days to show up. If you are new to the topic, start with what SEO is; this guide explains the machine SEO works with. For the practical order of work, see how to rank higher on Google.

Which search engines do people actually use?

In the United States, Google handled 85.19% of searches across all devices in September 2026, Bing 9.89%, Yahoo 2.64% and DuckDuckGo 1.75%, according to StatCounter. In Colombia, Google's share was 93.3%. For most businesses, that means Google first, with Bing worth a basic setup because it is the clear second.

Figures are for September 2026, all platforms, from StatCounter for the United States and Colombia. They measure page views coming from each engine, so treat them as a picture of habits, not an exact count of searches.

How does a search engine work?

A search engine works in three stages. First it crawls: automated programs visit pages and follow links to discover new ones. Then it indexes: it reads each page, groups duplicates and stores the best version. Finally it serves results: when someone searches, it picks matching pages from the index and orders them by relevance and quality.

1. 01

   Crawling

   Google's crawler is called Googlebot. Google's in-depth guide to how Search works explains that there is no central list of every page, so Google discovers URLs by following links from pages it already knows and from sitemaps that site owners submit. It also renders pages, running JavaScript the way a browser would, because many sites load content that way.

2. 02

   Indexing

   Google analyzes the text, images and key tags of each page. When several pages are very similar, it groups them and picks one canonical version, the one that may be shown in results. The same guide is clear that not every page Google processes gets indexed.

3. 03

   Serving results

   When someone searches, Google looks for matching pages in the index and returns the ones it judges most relevant and useful. The results depend on things like the person's location, language and device, which is why two people can see different results for the same words.

Two details from that guide matter to every business owner. Google does not guarantee it will crawl, index or show any page. And it does not accept payment to crawl a site more often or to rank it higher.

How does Google decide the order of results?

Google uses many automated ranking systems that look at hundreds of billions of pages and weigh signals such as the words on a page, links, freshness and spam. No single factor decides. Each system answers a different question, like whether a page is original, reliable or the best part of a page for a specific search.

Google publishes a guide to its ranking systems. A few of them explain a lot of what you see in results:

The practical reading: you cannot win with one trick. You need a page that is reachable, clearly about one topic, better than the alternatives and supported by real signals from other sites.

What changes when search engines answer with AI?

AI answers sit on top of the same index. Google's AI Overviews and AI Mode can run several related searches at once, which Google calls query fan-out, then show a summary with links. Google says there are no extra requirements: a page must be indexed and eligible to show a snippet. What changes is how often people click.

Google describes this in its page on AI features and your website. The click side was measured by Pew Research Center, using the browsing data of 900 US adults in March 2025. AI summaries appeared on 18% of the Google searches in the study. When a summary appeared, people clicked a traditional result in 8% of visits, compared with 15% when there was no summary, and they clicked a link inside the summary in about 1% of visits.

For a business, that means two jobs. Keep the basics solid so your pages are eligible at all, and make the first lines of each page answer the question clearly so an AI system can quote you. I go deeper in what AI Overviews mean for a small business.

What this means for your website

Once you see the three stages, most SEO problems sort themselves into one of them. Here is the short version I use when I review a site:

• Crawl: can Googlebot reach every important page through normal links? A firewall or security screen can block it. On one clinic site, removing that block took the average position from 13.5 to about 9.
• Crawl: is there an up-to-date XML sitemap submitted in Search Console?
• Index: does each page have one clear version, without near-duplicates competing with it?
• Index: does the Pages report in Search Console show your key pages as indexed?
• Rank: is each page clearly about one search, with a title and first paragraph that say so?
• Rank: do other sites, directories and reviews confirm that your business is real?

Crawl and index problems are technical SEO work, and they come first because nothing else counts until they are fixed. The technical SEO checklist goes through them one by one, and the clinic case study shows the firewall example in detail.

Should I optimize for Bing and other search engines too?

Yes, but you rarely need separate work. Bing, Yahoo and DuckDuckGo also crawl, index and rank, and they reward the same basics: reachable pages, clear content and real signals of trust. Verify your site in Bing Webmaster Tools, submit the same sitemap and check that nothing blocks its crawler. Then focus your effort on Google.

If you want to know where your own site stands at each of the three stages, start with the free 30-minute diagnosis on the home page, or read the full order of work in how to rank higher on Google.

Frequently asked questions

About the author

Juan José Giraldo is an SEO consultant in Medellín, Colombia, with 5+ years of experience. He works on technical and local SEO for 600+ US car dealerships at Reunion Marketing, an Inc. 5000 agency, and supervises the SEO of 18 US online stores with more than 3 million products at Prontomowers. Read more · LinkedIn.

Sources

1. Google Search Central, In-depth guide to how Google Search works
2. Google Search Central, A guide to Google Search ranking systems
3. StatCounter Global Stats, Search engine market share in Colombia (September 2026)
4. StatCounter Global Stats, Search engine market share in the United States (September 2026)
5. Google Search Central, AI features and your website
6. Pew Research Center, Google users are less likely to click on links when an AI summary appears (July 22, 2025)
7. Google Search Central, What is a sitemap