The dungeon spawn keys screen allows you to place a key you made previously using the keys action inside a room as a physical item that can then be picked up by other players when they reach this room.
It is a great way to secure part of your dungeon and make it so people have to find the keys to get further in to your masterpiece.
Select the key then either click the Place key button to place the selected key into the room or click the Delete Key button to delete any placed keys in the room.
You may only have one key placed in any one room at any time so plan your dungeon accordingly. Also these keys do not show up on the dungeon items screen this means the only way to delete them is via the spawn keys screen.