As a company, Google focuses on three key areas: Search, Ads and Apps. Search is our core technology; ads are our central business proposition; and apps are the umbrella over our web-based software that you can access anywhere, any time. While each of these has a lot of technology under the hood, the basic tenets for Search, Ads and Apps are very simple. We’ve created some short videos explaining the principles behind our core services. For more information or to share your thoughts, visit our Help Forum.
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Check this link for more info http://computer.howstuffworks.com/internet/basics/search-engine1.htm