Friend clickbank is not a ppc program it is far from it. Clickbank is a affiliate program. You sell other people's digital products(mostly crappy ebooks and softwares) and get a percentage of their sales.
Join and get a unique affiliate link with every product and put it on your site. If someone clicks on it and buys - you get a percentage of the sale.
you get into clickbank affiliate and offer other product , you get commission , this affiliate system
Why don't you just go to the help center and do a bit of reading? http://www.clickbank.com/help/ That page will tell you everything you need to know.
What the heck.. So instead of just going to their website and reading what they're all about, you come to this forum and waste our time? You will never make any money if you're expecting everyone to spoon feed you information.