How do you use looking for party tool?

I've looked at it ingame, and I can't quite figure it out, anyone can walk me thru it?

Nobody use it, so thers truly not much you can do with it.

use it as a global advertizing tool

I use it and not like an global advertising tool.
Open the room party window, select the lvls that u want in ur party, enter an apropriate description (raid LF tank lvl xx to lvl yy), and thats it. Ppl that are in the selected range lvl will be able to enter the party room, u can chat with them. If they are the ones u need u can send an invitation.
The party invitation can not send from party room window (at least this is what I know)

Dont know about all servers but on Hindemith its always 5-10 parties with a room there.