Google AdSense is a program of Google Inc. that allows you in the Google Network of content sites to serve automatic text and media adverts that are targeted to site content and audience. These adverts are maintained by Google, and they can generate revenue on either a per-click or per-impression basis.
It is easy to figure out that Advertisers pay Google to promote their products and services through the Google Adwords program. The ads are meaning the content typically fits with the theme of the site or the page they are displayed on. For example, A blog about Real Estate would typically have Google Adsense ads that relate to real estate,Work from Home blogs will usually display ads relating to home businesses.
Here is their website:http://www.google.com/adsense
When your website have visitors over 100 per day,i advise you go to google adsense and creat a account.