Google AdSense is a great way to supplement your web site's income! So what exactly is Google AdSense?
This is a program run by Google that pays you per click. You sign up free, paste a little bit of code on your website and every time someone clicks the links on your site, you get paid a certain amount per click.
Some clicks are worth higher than others depending on the "keyword" that the ad is targetting. What does this mean? Google AdSense are "contextual based" ads, meaning that they display the links for people to click on based on the context of your website.
For example if you have a website about "tennis" then the ads Google AdSense will display will be all about tennis. So if the text on your site that Google is basing their AdSense ads on is for "tennis balls", then the keyword phrase "tennis balls" may be paying higher per click than "tennis racket".
Read More at : http://www.associatedcontent.com/article/26788/how_to_earn_more_with_adsense.html