You can pay google to have a sponsored link for particular keywords. You can also participate in their link exchange program which generates cash for you. The programs you are both interested in are AdWords, and AdSense. You can find more information about both here: https://adwords.google.com
and for AdSense: http://www.google.com/services/adsense_tour/
Both are great programs for driving hits to your web site and earning cash. It also helps if your site is optimized for their search engine.
Both of them are Pay-per-Click advertisements. For example:
I have a website about manufacturing computer components. I can purchase sponsored linkage when certain keywords are typed into a google search engine. If I purchase the following keywords for my site:
Computers, computer parts, electronics, computer components, ohio, united states, streetsboro, portage county.
Those keywords have different values when someone clicks on them. Pay per click means that when someone types in a search with any of the given keywords, your site pops up, and they click your site, you will pay x amount of dollars based on the keywords that drove them to your site. Computers as a result will cost me more money than portage county.