Connected to this screw should be a red, black, or blue covered wire. If you have properly turned off the power, there should be no signs of voltage.
Remove the lock-nut from the cable clamp. Push the cable clamp through the hole. The side that comes through the bottom should have spiral edges for screwing it in. Tighten the lock-nut back around the cable clamp by placing it at the underside of the clamp where you see the spiral edges and screwing it in with Channel-Lock pliers.
Take a neutral wire and cut away about a centimeter of the covering at the end of the wire. Use your flathead screwdriver to unscrew one of the screws and then push the wire through. Screw it back in after you have inserted the neutral wire.
You should find a list of acceptable circuit breakers you can use. Make sure that your circuit breaker is of acceptable size and voltage.
