If you don’t know about Google AdWords then here is a quick description about Google AdWords :
Google AdWords is an advertising program. AdWords ads are relevant ads that appear alongside or above the search results in response to searches on Google. With AdWords you are promoting yourself to interested prospects right when they are searching for just what you offer.
To get your free Google AdWords coupon, sign in to your Google webmasters tools and check your messages inbox. You will find a message there which contains your free code that will credit $100 into your AdWords account.
Thanks to Blogote for this info.