Switch off the main power to the entire house. Often the circuit breaker will have a main switch at the top, otherwise you will need to switch off the power where it connects to the house at the electrical meter. Never work on a live circuit.
Remove the access panel for the circuit breaker box. There will be screws that need to be removed so you can get to the wiring inside the breaker box. Touch one of the probes from your circuit meter to the common bus bar in the breaker box. This is where all of the white wires are screwed. Touch the other probe to the bare metal of a red or black wire. If any voltage registers, then the power is still on. If you can't figure out how to turn it off, call an electrician. You life may depend on it.
Break out the knockout hole in the breaker box that is closest to where you want to run the new circuit.
Feed the 3-wire plus ground cable into the hole and then remove the last 12 inches of outer sheathing to expose the individual wires. Strip the last half-inch of insulation from each of the constituent wires.
Screw the green or bare wire to the ground bus bar. Screw the white wire to the common bus bar. Insert the black wire into one of the terminals on the new 2-pole EPD and secure it with the screw. Insert the red wire into the other terminal and screw it in place.
Press the EPD into the next available slot on the breaker bus bar. Some will snap into place while others must be screwed in. The wires should face out away from the middle.