AdWords is a pay-per-click (PPC) advertising program. Advertisers specify keywords they want to target and bid on them. Their ad will appear on the Google search page when users search for the same keywords. Ads with higher bid amounts will generally appear higher on the page. If a user clicks the advertisement, the advertiser will be charged the bid amount. These can be as low as $0.05 and go as high as $30 per click for highly competitive keywords.
Google AdWords is the largest advertising opportunity on the Internet today. Other search engines offer pay per click services but, considering Google refers up to 85% of search traffic, this is the best option.
If you don't show up on Google, you don't exist. If you want a reliable way of showing up on Google, participating in their sponsored listings program, Google AdWords, is the way to go.