Electrical cable is available with 3 or 4 wires running through the sheathing. Cable with 3 wires is referred to with labels like 14/2 and 12/2, where the two represents the black and white, current carrying wires in the cable. The other wire, the ground wire, is ignored in this labeling. Cable with 4 wires is referred to as 14/3 or 12/3 cable. Here 3 wires carry electricity, the black, red and white. All household cable is available with 2 or 3 current carrying wires and one ground.
Another switch you may find in your home is a 4-way switch. These have four terminal screws and a fifth green one for a ground wire. Four-way switches are used between two 3-way switches to control lights from 3 or more locations. This can be handy if you have a large room with several entrances requiring light control from multiple locations.
Press a small board against the bottom of the outlet box to hold it flush with the ceiling while attaching the support assembly to the joists. Working through the channel, drive deck screws or nails through the holes in the metal hangers and into the joist. Use four screws on both ends of the support, two on each side of the hangers.
Locate the two joists nearest the new fixture location using a stud finder or tap on the wallboard until the sound indicates the general location of the joists. Use a drill and an eighth inch bit to drill through the plaster where the joists are estimated to be. Drill holes at 1" intervals until you meet resistance and wood from the joist is ejected. Mark the location of each joist with a pencil mark.