The "common" is the "neutral" or "ground" wire, depending on the type of circuit. In normal US residential wiring, you'll have a black "hot" wire, a white "neutral" or "common" wire, and a green or bare "ground" wire.

What does common mean in electricity?

The common wire is normally the white wire, at least in the United States, and is often called the neutral wire. It's also called common because all circuits in the house typically have the white wires tied together, which means every circuit has that wire in common.

Does the hot wire go on the common screw?

The black (hot) wire goes to the brass screw or into the hole in the back of the device on the same side as the brass screw. This wire is sometimes red. The green or bare copper (ground) wire, if the device has one, attaches to the green screw terminal on the switch or to the electrical box.