You are supposed to be able to buy the board and put it on the wall of your room. Then you access the broker system through it, selling stuff via the board. All things you sell will appear on all brokers in town. People will be able to buy the stuff from the broker at a 20% mark-up or come to your room (the location of which is with each item on the description). You will need to stay in the room during the sale so it's really only something you can currently do if you plan to leave your toon logged on overnight or something.
I tried to buy the board from three vendors last night and it wouldnt let me. I'm assuming it's bugged though I have seen items for sale on brokers so someone must have managed to buy a board.
I have submitted a bug report and here's hoping it's fixed soon, cos i have loads I wnat to sell and am running out of space rapidly
Hope that helps.
Minky