Boxes come in two basic types Metal and Plastic.
For general residential construction the choice is left up to the contractor and if the box is not exposed then it will most often be a plastic box. Exposed boxes like the ones found in unfinished basements and outside the home are made of metal this is to reduce the risk of breaking the box and then having exposed wires.

Installing …

Electricity can be dangerous.

You should always turn the circuit off at the breaker box or remove any fuse to a circuit you are working on.

One easy way to find the circuit is to plug-in a radio in to the branch you want to work on then turn off breakers at the main box until the noise stops. Once the circuit is cold you want to tape that circuit breaker in the off position and hang a sign over it …