How Do Search Engines Work? All About Ranking and Bidding

How do search engines rank URLs when there are as many as 50 billion pages live on the internet? MirageC / Getty Images

If you've ever typed a question into Google, Bing, Startpage or DuckDuckGo, you've seen the slick results page that pops up. But what makes those results tick? How do search engines work?

That simple query leads to a world of bots, algorithms and auctions that help you find cat videos or track down the nearest sushi spot.

Most search engines aim to answer your query as quickly and accurately as possible. To do that, they rely on a multi-step process: crawling, indexing, ranking and serving results. Understanding that process means understanding the backbone of how we navigate the web.

Crawling the World Wide Web

Search engines start with crawling. A search engine crawler — often called a bot or spider — roams the internet collecting data. These bots follow links from page to page, fetching copies of web pages and storing them in huge data centers.

Think of it like a postal worker mapping every mailbox in a city. Web crawlers look at all the pages they can find, discovering new pages, noting changes to old ones and identifying dead links.

Google Search works this way, constantly scanning for updates and using the Google Search Console to help site owners manage visibility.

Building a Search Index

phone — When you look up that random curiosity, are you also thinking about the search engine crawling an unfathomable amount of information to provide an answer? Tatiana Meteleva / Getty Images

Once crawlers fetch pages, search engines move to indexing. This is how they organize information to deliver relevant results fast. The search index is like a massive digital library catalog where every word is filed away.

Indexing algorithms analyze everything on a page: text, images, metadata and inbound links (links pointing to the page). They also sometimes identify the canonical page, which helps avoid duplicate pages clogging the index.

Search engines analyze page speed, mobile usability and other factors to determine how pages should rank in search results.

If you're wondering how many pages are in a search engine's index, the answer is trillions. Google alone processes roughly 14 billion web searches daily.

Ranking Web Pages

When you type in a user's query, the search engine analyzes it and fetches matches from its index. But the results aren't random. Search engine algorithms rank web pages based on relevance and authority.

Ranking considers dozens — sometimes hundreds — of signals. These include keyword usage, inbound links, freshness of content and more.

The goal is to surface relevant results at the top of the search engine results page (SERP). Local search, search history and even your device type can tweak what shows up.

Google determines relevance using tools like BERT and RankBrain, which help interpret natural language. This is how most search engines aim to understand not just keywords but user intent.

Monetizing Search Results

Most popular search engines (including Google) monetize through ads. When you use the search bar, you often see ads alongside organic results. These are part of the pay-per-click (PPC) model, where advertisers bid to show up for specific queries.

Search engines rank ads in a separate auction. Factors include the advertiser's bid and the quality score, which measures ad relevance and landing page experience.

The result: Google Search Engine makes billions annually, turning user searches into revenue.

Optimizing for Search

Search engine optimization (SEO) is the art and science of helping your own site appear higher in search engine results. It involves making your site easier for bots to crawl, improving page speed and creating relevant content.

Avoid keyword stuffing, which can get your page penalized. Instead, focus on what makes content helpful to users. The goal is to enable users to find what they're looking for while also signaling to search engine bots that your site is trustworthy.

For site owners, tools like Google Search Console and resources like Search Engine Journal offer guidance on indexing and ranking. The ultimate aim: to help search engines find, understand and rank your content.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.