Google search engine is very powerful for search any site. But how it is possible?? I am very astound to see its power. It can gave us any things of the world in one moment. What is the source? How it is possible?
The Google has its large database to store each and every information in fragmented way. So, each and every word you type is matched by Google bots to bring you the max possible answers to your query.
To know how Google works, why don't you follow google's guide - http://www.googleguide.com/google_works.html