When you Search, Google looks through hundreds of billions of webpages and other content stored in our Search index to find helpful information — more information than all of the libraries of the world. Most of our Search index is built through the work of software known as crawlers.

Once Google discovers a page's URL, it may visit (or "crawl") the page to find out what's on it. We use a huge set of computers to crawl billions of pages on the web. The program that does the fetching is called Googlebot (also known as a crawler, robot, bot, or spider).

To give you the most useful information, Search algorithms look at many factors and signals, including the words of your query, relevance and usability of pages, expertise of sources, and your location and settings. The weight applied to each factor varies depending on the nature of your query.