This post will only remain on the front page for a day but here is all that you need to know.
You can list three items on the auction house - however each item that you list the tax on that sale increases.
To list an item on the auction house do /minebay sell [price] whilst holding in your hand what you'd like to sell and you will see this GUI.
(For example, hold 1 diamond and type /minebay sell 100)
Choose a room to list your item and that's it!
You can only list one item per room, each room has a higher tax than the previous.
If you're looking to browse available items /ah will open this menu, you will however need to click on each room and reissue the command.
We hope that you like this feature and we're welcome to feedback. Expect some tweaks to this system over the coming weeks.