I believe how the mechanism works is that you have to give them a link with a referrer ID. When they visit the site, a cookie is added and if they register while that cookie is still alive, you get credit. There may also be a way to enter someone's name in the registration form... it's been kinda a while since I looked.
You'd give them the ID in the link like this:
http://www.eq2flames.com/?referrerid=####
It could link to any place really within EQ2Flames, it just needs that referrerid in the URL.
Finding your Referral ID is a bit harder since they made the forums search engine friendly, but hovering over your photos # link still shows your user ID and that's what you use.