Go into the General Room (or the general window or any of the other rooms established).

There's a Tab called "Rooms". Click it, and it will list the rooms and at the bottom there is a button called "Create new room". Just type in whatever name you want for the room and if you want it to be password protected (then you need to enter a password) ... and Voila! Your own homemade room.

Hope that helps and I didn't ramble.