You go to the hotel and they will give you your room keys. Each person will receive one. You then take the hotel key to the express pass kiosk in the hotel. You insert your room key and the kiosk will take your photo and spit out an express pass with your photo on it.
Also in the lobby with the express pass kiosks, is the park ticket kiosk. You insert your credit card (for ID purposes) and the code that is given to you in your reservations and it will spit out your tickets. This can all be done at any time.