How do my affiliates get the link they put on their site so they get credit?

When an affiliate signs up to be an affiliate, where do they get their affiliate url so they can put it on their website and get credit for everyone the send to my store?

First, make sure you set up an Affiliate block in Design->Blocks. Your affiliate will see this block when they log in into the storefront and will be able to choose the banners they wish to use.