Basically measure the distance from the box and your outlet. Take the wires through to the box and then cut the wire to the let you need it. Then you want to push the wires into the box.
You have to be sure you're wiring to a 15-amp fuse or circuit breaker at the control panel box. You want to be sure that you don't have too many outlets and light switches on the circuit as to avoid blowing fuses or tripping breakers.
