Ok, so you're playing The Burning Crusade (of course, unless you're doing Beta testing, you're not REALLY playing, but just go along with me here...it'll be useful info when you DO get to play for real).

So you're playing The Burning Brusade and you need a worthy group of adventurers to go with you on a particularly dangerous quest, journey, adventure, or whatever. Well, in the new expansion pack, you'll be able to use the "Looking for Group" interface to find players who want to go with you and who meet certain criteria you have set for your adventurers. Here's how it'll work:
There will be a new icon added to your action bar, next to the Social button. When you click it, it will open a window that will ask whether you want to start a new group or join one that's already being assembled. When you make your selection, you'll either see the "Looking for Group" interface or the "Looking for More" interface. There are tabs at the bottom that allow you to switch between the two. What's the difference between the two interfaces? "Looking for Group" adds individual players to a pool of other players looking for a group and matches them up according to preferences they have set. "Looking for More" gives already formed groups the ability to search out additional members to complete their group.

I'm fairly certain that this will be a popular tool for the new expansion, because, from what I understand, you'll be able to specify certain characteristics (maybe even stats?) that you want in your group members. It will be interesting to see how this works out when The Burning Crusade is finally available to all of us for play.