*As an affiliate, you can buy pay-per-click ads based on certain key phrases and drive traffic to your affiliate through them.
Cost per click is the cost an advertiser pays for each click on their ad (this is performance advertising). If the ad doesn't perform, you don't pay anything. You can buy cost-per-click ads as an affiliate program promotion tool on most search engines, as well as individual sites. Generally, bids are placed (what someone is willing to pay per click) and the search engine will feature the top bidder as "sponsored" links on their search results page.