Choose the best location for the lock on your desk. The location needs to be out of the way, but also accessible. Place the main part of the lock on the desk drawer and mark the screw hold locations by using a pen or pencil through the holes. Mark the bolt piece location on the frame of the desk at the same time.
Drill holes into the marked spots on the desk drawer and frame. Make sure the drill bit is a size smaller than the width of the screws so that the screws will be able to go in tight.
Screw the lock into the drawer using the screws that came with it. Tighten the screws down using a screwdriver. Screw the bolt into the frame of the desk, tightening it down with a screwdriver. Bolt the lock to test the security.