There are two ways to do it:
1. Go the the FAQ, and there is an area about referrals. You can
click here to go there directly.
2. When you friend is signing up, there is a space name referrer. Have them input your user name (wdwjeff), and it works just as well.
I think using the way described in the FAQ is better, it will take them right to forum home page, and then they just click on register. Your name will already be in the registration form and they won't have to remember to put your name in. Does that make sense?