This diagram is similar to the one above, but the switch comes before the new light in the circuit. New cable is run from the receptacle to the new switch location and from there to the light location. The switch may also be added in the the same box with the receptacle as in the diagrams at this link, where the two are installed in a double-gang electrical box.
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.
The neutral wire in this circuit is taken from the receptacle and spliced to the white on the new cable, and to a pigtail that runs back to the receptacle. The hot is spliced to the black cable wire and a pigtail back to hot on the receptacle.
This circuit breaker wiring diagram illustrates installing a 50 amp circuit breaker for a 240 volt circuit. The 6 gauge cable for this circuit has 3 conductors and 1 ground. A 50 amp circuit like this is used for clothes dryers and new kitchen range installations.