This diagram illustrates some of the most common circuits found in a typical 200 amp circuit breaker box. The breakers are installed in a service panel so that contact is made with one of two hot bus bars that run down the middle of the box. The hot wire for a circuit is connected to the breaker by a set screw on the base.
This wiring diagram illustrates wiring a light switch to control an existing receptacle outlet. The source is at the receptacle and a switch loop is added to a new switch. The hot source wire is removed from the receptacle and spliced to the red wire running to the switch. The black wire to the switch connects to the hot on the receptacle.
Another, more permanent, repair for an old doorbell circuit is to use a small ac adapter in place of the battery. Most people will have an AC adapter left after an old radio or similar device has long since died. Look for an output of 10 to 16 volts printed on the side of the adapter casing. Current ratings will typically be very low from these adapters, around 500mA, making them perfect to power the doorbell circuit. All that is needed is a conveniently located receptacle to plug the adapter in.
To add a new outlet to a group of receptacles already in place, splice the new wires to one set of wires on one of the existing receptacles. In this diagram each receptacle is wired to the next using the terminals to pass the voltage along. To provide voltage to a new receptacle, remove the wires from one set of terminals on the existing outlet and splice in the new wires and a pigtail back to each terminal.