How Google Search Works Video
Here is a video released by Google to explain how the Google search actualy do the job of searching. When we hit the search button on the Google we are not not searching the web, instead it is searchin the index of the web stored in the servers of Google. Google creates an index of the web pages it can find and it returns the most relevant results by evaluating more than 200 quality factors. Google’s search results are impartial, they’re clearly separated from ads and they’re returned in less than half a second.
Indexing is done by a software called spiders. Spiders analyze a web page and index everything on that particular page to the Google’s servers. Then it fetches other pages linked from that page and do the same job in those pages. This process is called crawling. As the spider crawls the web, the more and more web pages get indexed by the Google.
All the activity involved in a searching is beautifully illustrated on this video.

