Google AdSense is an advertising program that was launched in the middle of 2003 by Google, the popular search engine. Google acts as an intermediary between a vast number of advertisers and an equally impressive number of website owners. AdSense is an ad serving application run by Google Inc. Website owners can enroll in this program to enable text, image, and video advertisements on their websites. These advertisements are administered by Google and generate revenue on either a per-click or per-impression basis.
In short, If you have a website or a blog having good content and atleast 6 month old then you can earn from your website or blog using google adsense . You can register on google adsense, wait for approval, take code after approval and paste on your website . If any visitor will visit adsense links then you will be paid for that. COmplete detail visit here: www.google.com/adsense