[gearmesh, inc.]

A 3 way switch is basically a single pole/double throw switch. A 3 way switch will not have an on/off indication, as it can pass current in either position. One of the three screws will be a common, and is usually darker in color than the other two. The other two can only be switched to the common one at a time, determined by the lever position. If you want 2 place control of a light or outlet, you need two 3 way switches.

For 3 or more place control for electrical devices in your McMansion, you need a 4 way switch in the circuit between your end two 3 way switches. A 4 way switch has 4 terminals on it. One state of a 4 way switch connects the side terminals to each other for a 2 pole straight through connection. The other state connects each individual side terminal to the opposite one diagonally across from it. You can also think of it as a reversing switch. For more than 3 place control, you can put as many 4 way switches in the circuit between your end two 3 way switches.