Belts with built in loops near the buckle work best.
Tighten the belt to the prefered tightness on your wrist and mark off where the small skinny part of the buckle needs to push through the belt.
Punch a small hole where you had marked on the belt and then push the stick on the buckle through.
Feed the rest of the belt through the built in loops near the buckle and mark off where the belt comes out through the loops.
With the utility knife, make a clean, straight cut along the belt where you had maked it. Now your Buckle Cuff should is done.
Alternatively, if the belt has no built in loops near the buckle make a mark an inch or so after the hole you just made. Then cut off the belt from that point.