1. People give their Ads to Google (and pay for it) 2. Google has them in Adsense, where you can apply 3. If you have a site about golf, then the Google code you put on your site will (most likely) shows ads related to Golf 4. When someone clicks, you get 0.1 cent or even a few dollars When you get 100$, they send you a cheque. You must not click on your own ads or tell people to do so. No warez, porn sites etc. Create your own content and don't spam.