Google AdWords is a pay-per-click service that lets you create and run ads for your business, quickly and simply.
AdWords ads are displayed along with search results when someone searches Google using one of your keywords. Ads appear under 'Sponsored links' in the side column of a search page, and may also appear in additional positions above the free search results. This means that you'll be advertising to an audience that's already interested in your business. You can also choose to display your ads on Display Network sites in the Google Network.
Just visit http://www.google.com/adwords to get started.