If you type a request for Tiger Woods, you'll get web sites listed according to how many times those words appear. That's no guarantee of quality and is open to abuse. If you have a Tiger Woods site for fans, just type his name into the source code thousands of times and search engines will list your site first. Google's answer is to treat the Internet as a democracy with links between web sites as the votes. The most linked-to web sites rise to the top of Google's search results.
More weight is given to sites with millions of links themselves.
Popularity equals quality, thus a computer program can evaluate what's the good stuff. It seems to work. Google licenses the search engine to other dotcoms but they charge per search, rather than the usual flat fee. That's why they expect to turn a profit soon. The whole idea of Goggle is to get you on and off the site as quickly as possible.