google ads work by you submitting to Google your site content and the sort of thing that people viewing your site would be likely to buy. Google then passes this information on to relavent companies that advertise on this space, I think that you get paid a certain amount of the profit made by these companies, quite a good scheme, and not a bad earned if you get lots of people on your site.
"If I seem to act unkind, its only me and not my mind" I Want To Tell You, The Beatles, Revolver
"When I am king, you will be first against the wall" Paranoid Android, Radiohead, OK Computer
There are two types of people, those who hate Microsoft, and those who work for it...
Possibly a Mac Convert