The Google WebMaster Tool is a function built by Google, which makes the websearch easier. With the Google WebMaster Tool you can index your website and make it more easy to find for the internet users.

During a websearch, Google looks through every registered website and compares their keywords with the words you have entered while searching. The most important things  are the title-tag and the keyword-tag of each website.
Furthermore the PageRank is important. The PageRank is becomes better and better when there are more hyperlinks referring to your website. Google tries to ignor invalid spam links to deliver good search results.