The Auction House allows players to list items for sale. As a guest you are able to list one item at a time, but the more you rank up the more items you'll be able to list on the Auction House.
Once you list an item on the Auction House it stays on there for a week, or until someone buys it. Listed or expired items can be returned.
To see all the items that are listed on the Auction House do /ah. If you see an item you like and you are able to purchase, right click the item. Then right click again the item to confirm your purchase.
Selling an is almost as easy as buying one. First hold the item you are wanting to sell in your main hand, then type /ah sell
price being the price you are wanting to sell your item for and
amount being the amount of items you are waning to list. For example: I'd like to list 64 iron blocks on the auction house for 6400. I'd first hold the item in my main hand and then type /ah sell 6400.
If you listed an item you didn't want to sell, or you listed it for too much you can easily cancel the item. First open the Auction House (/ah), then click the diamond at the bottom left, then click the item you'd like back. The item should now be in your inventory!
/ah Opens the Auction House.
List an item on the Auction House.
/ah return Return expired items back to your inventory.
/ah sold Shows all the items you've ever sold using the Auction House.
/ah help Shows some more commands about the Auction House.