Turn off the main breaker and remove the service panel cover. Use a screwdriver to open and remove a circular knockout on the side of the service panel. Insert a NM connector into the hole so the cable will not get cut on the sharp panel edge. Slide enough cable through the connector to reach to the circuit breaker, fasten the connector onto the cable and strip the sheath off the part of the cable which is inside the panel in order to expose the wires. Bending the wires as little as possible, run them along the outer edge of the panel to the location for the circuit breaker.
Slide the bare ground wire under a screw on the neutral bus and tighten it in place. Strip about 1/2-inch of insulation off the ends of the black and white wires. Wrap some black electrical tape around the end of the white wire to indicate that it is a hot wire rather than a neutral wire. Insert each wire into the breaker and tighten the screws snugly. Ensure there is no more than 1/4-inch of bare wire showing outside the breaker.
Hook the wire end of the breaker under the notch in the service panel and push the other end onto the bus in the center of the panel until it is seated firmly. Replace the service panel cover and turn the power on.