A sponsor runs a pay site and surfers, using their credit cards, buy subscriptions from the site in order to view the porn. As an affiliate, you can refer surfers from your little site and earn a commission. Sponsors usually offer affiliates free content so that you don't have to photograph your own models. If you go to a porn pay site there is usually a webmaster link at the bottom where you can sign up. Greenguy has a comprehensive guide to porn sponsors here:
http://www.greenguysboard.com/resour...ors/index.html