After you've placed the order, we assign a PRO player with Knight-Captain Murky item in his inventory. He works according to the agreed schedule and will contact you in-game to trade you Knight-Captain Murky.
As soon as you receive Knight-Captain Murky you can learn it from your inventory, and it will become available to all the characters on your account. If Knight-Captain Murky is the Blizzcon promotion code, you will receive a digital code to redeem at your battle.net account page.