When you do a search on Google MSN or Yahoo, you’ll notice “sponsored links” appearing on the right side of the page, and frequently at the top of the page as well. Those are called, pay per click ads, and you are only charged When someone clicks on the actual advertisement and not when it is displayed.

Whether you appear at the top or at the bottom used to be based simply on how much you were willing to pay. If you need more than the next advertiser than your ad appeared above theirs. It was simple.