its a free application for your website or blog to generate a good amount of money just create a account on adsense and put a code on your site or blog then it will automatically generate a good amount of revenue for your website
Google AdSense is a free, simple way for website publishers of all sizes to earn money by displaying targeted Google ads on their websites. AdSense also lets you provide Google search to your site users, while earning money by displaying Google ads on the search results pages.
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. Google beta tested a cost-per-action service, but discontinued it in October 2008 in favor of a DoubleClick offering (also owned by Google).[2]
This is correct information for google adsense. Need to select your niche and do work according to that.
Easy, sign up to Adsense, and just place the ad code from your account into your website, Google will automatically scan your website in order to display relevant adverts.
You can use it to put ads onto your website which will earn you money once your traffic/users click on them, It's best to go to Google adsense it's self in the FAQ for an example to see on how to fully use it all the answers are there.