*THIS KEY HAS A ONE TIME USE* Edit
The key is used to allow players to access arcane doors in SMP
Hold the key in your hand then right click on the door you want to allow your friends to open/close. This will create an 'enchanted' key with the coordinates of the door in question. Simply give the key to whoever needs to access the door; when they right-click the door, the key will disappear, and they will be able to open and close the door.