Google Ad Words is Pay Per Click advertising. That means that you only pay when someone clicks your ad to go to uyour website. You set how much money you want to spend and what keywords you want to use. When people search on Google using one of your keywords, your ad may appear next to the search results. Now you’re advertising to an audience that’s already interested in you. Set your ads to appear only to people searching in a particular city, region, or country. Now it’s easy to target online customers within 20 miles of your front door or across the world.
Start Here: http://adwords.google.com