Here's a really quidck explanation of Tracfone referrals, how they work, what they do, and what double referrals can do.
First one guy puts in his Trac's serial number into an online form and sends (via that form) notes to some email addresses telling how great Tracfone is and to join. The person on the other end clicks on the link and activates by it. They get a set of 100 promo minutes and so does the other guy. Which act like regular 100-pack ESN minutes except the referred person doesn't get any extra days on his expiration I think.
Double referrals work similarly, except that both people are unactivated. Thus people can be both the referral than the referrer. It's that simple.