Affiliates & Marketpress: Is there a tutorial on setting this up?

I am looking for some general setup instructions for Affiliates. Here are some specific questions:
Where does a potential affiliate sign-up?

Once signed up, how does he/she collect money?

How do I ensure that the affiliate is only paid a percentage of a purchase directly referred from their website or email?

I will continue looking on the support forum. If there is an answered similar post, please save the typing and send a link.

Thanks!