Commision Junction is a site you can sign up for various kick backs for commissions on helping sell products. Our product has a sign up on there for you to get a kick back for helping to sell the product
You would have to sign up at commission junction for the Photopost company thing. Commission Junction can assist you with how to use your site. Once you officially apply for a commission with a company there is a url you are given which is your affiliate url and this is what you place in that setting in admin.