Ok, this appears to be pretty simple. Also, it is something you HAVE to do in order to have access to guild forums.
(1) Once you have registered, click on your username;
(2) Click the "Characters" tab;
(3) Click the "Add Character" button;
(4) in the box that pops up, under "Game", select "World of Warcraft". When you have made that selection, the "Server" box should automatically populate Garrosh for you;
(5) Type your character name in the "Character Name" box, and click the "Add Character" button at the bottom;
(6) Repeat for as many of your toons as you would like. When you have finished with that, note that you can click a link that says "Make main". You can also log in under that toon.
Omg, I love this site - SO much easier, quicker than the Curse site.