The single pole light switch is the most common, one light switch controlling one or more light fixtures.
A 3-way light switch is where you can control one or more lights with two switches (common scenario at the top and bottom of stairs).
Where the word supply is used in the guides below, refers to the main wire supplying the electric to the switch.
To prepare the wires to be connected to the light switch strip the plastic off the ends of the wire a half inch down from the end.
In the first picture below you see three wires sticking out of the outlet box. One wire supplys electric from the breaker box, another wire feeds electricity to a outlet, and the other wire goes to the light fixture.
As shown below in the last picture the supply wire and the wire going to the outlet are connected to the same screw. Then the wire feeding the light fixture goes to the other screw.