A circuit breaker or fuse box. Electricity enters the household circuitry through the service panel and is distributed from there through circuit breakers or fuses to branch circuits.
A pipe through which an electrical cable is run to protect it from damage. Conduit is available in metal and pvc plastic. Conduit is required in places like unfinished basements where electrical wiring is exposed and therefore vulnerable to damage.
Thread the connector clockwise onto the twisted wires, being sure no bare copper is exposed at the bottom. Pull gently on the connector to be sure it’s secure. You can wrap electrical tape around the wires and cap for extra security or just push the splices into the back of the box and attach the cover plate.
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.