What is the purpose of a switch in a lighting circuit, specifically when it comes to controlling the flow of electricity, and how does it differ from a 3-way switch?

The purpose of a switch in a lighting circuit is to control the flow of electricity to turn the lights on or off. A regular switch has two positions - on and off. A 3-way switch, on the other hand, allows control of a light fixture from two different locations, such as at the top and bottom of a staircase.