Shut off the main power switch to your home. This is located at the top of the circuit breaker panel and is marked as "Main." Test the lights and outlets in your home to be sure you've turned all the power off.
Remove the screws on the front of the circuit breaker's metal panel. Take the panel off and set it aside.
Loosen the two screws at an empty circuit breaker location on the panel. Slide the ends of the white wire from the new electrical cable under the right nut and the black under the left. Tighten the screws.
Line up the new circuit breaker with the tabs located behind the panel. Push the breaker firmly into the tabs until it clicks into position. Turn the circuit breaker to the "Off" position. Leave it off until all the wiring is completed.
Pry out the knock-out panel on the circuit breaker panel that corresponds with the position of the new breaker. Place the panel back onto the box and attach it with the screws.
Turn the home's power back on.