You can Buy & Sell your items in the Auction House!
To Access the Auction House, type "/AH"
You'll be greeted with a GUI where you can choose to list an item, buy an item, sort listings, and collect your expired items! You can list anything you like, for as much as you like!
To list an item, first make sure it's in your hand. Then type "/AH sell [price]"
For example, if you'd like to sell your diamond pick with mending enchantment, hold it in your hand and type "/AH Sell 1000". The pick will be listed for $1000.
To see which items you are selling, type "/AH Selling". You can see items you've sold recently by typing "/AH sold".
Expired Listings (listing that have run out of time) can be collected by typing "/AH Expired" or "/AH Return."
To cancel ALL of your listings, type "/AH cancel"