Affiliate plugin and purchase link

HI - I've implemented Affiliates on my page ... it tracks visitors per affiliate, but I can't figure out how to get it to track sales. All affiliate links are directed to http://members.websitebliss.com/16/
But when someone clicks on the 'purchase' link on that page, it's not recorded by the Affiliates plugin. How do I tell the Affiliates plugin what the purchase link is?? Thanks!