Google is now so powerful that most people think Google and the Internet are the same thing. But there are other search providers that are still widly used, such as Yahoo and Bing.
Each of these search providers work in slightly different ways and produce different results. The problem with Google is that this mult-billion- dollar company distorts the search results because of the amount of paid-for advertising it includes - and it is not necessarily obvious which websites appear on your screen because of Google's paid-for services.
One of the reasons Google provides free email via Gmail is in order to scan all your private emails for information it can sell to advertisers.
Search result on Google (more so than the other search providers) can therefore be divided into two catagories: paid for and not paid for.
Dealing firstly with the issue of not paid for search listings: the things that ensure your website climbs up the listings and shows at or near the top are itemised HERE
The next page explains a little about how Google works.