There are two types of major Pay per Click engines. The first one is based on matching keywords that is called sponsored match and the second one is called content match. In basic Web design the Keyword PPC is more favored among the two since it helps you display your website on the search engine itself. 

Of course there is a few other Pay per Click engines but all of them contain one or other features of the above two. Constant improvements results in search engines falling into more than one category having the characteristics that is a combination of two or more categories. One important aspect is to remember that it does not matter how much traffic visits the site where your ad is displayed, you generate revenue only when some viewer clicks on the ad itself. The best Pay per click advice for you therefore is to design your model in such a way that more and more people are attracted in clicking on your ad. 

Keywords could be words, phrases or combination of such with numerical. When a visitor clicks on one of the keywords, the search engine displays the list of advertisers in order of the amount of bids they have put. Sites like the National Homebuyers follow this principle to the hilt and come out with near perfect Pay per Click management system. 

The most notable search engines that use the PPC keyword are Google, Yahoo, Looksmart, Yandex, Ask, MSN, and Baidu.