The nipple allows you to hook a pip from the nipple into your wastegate, allowing it to open the gate once the pressure is enough to open it.
Without running this line to your wastegate, the turbo will essentially free boost, and destroy itself (and possibly your motor) in no time.
I suggest you go into supercheap, explain you want a brass nipple vacuum fitting to screw into your intercooler piping. You shouldnt have too much trouble being pointed in the right direction.