It is a dark room with no light, someone lights a candle to brighten the scene. Generations later you just flip a switch to power a light bulb. What is making this work? Well inside a lightbulb is a bunch of wires and batteries making something called a circuit. The main parts of a circuit are positive and negative wires, a light bulb, a switch and a battery.
A circuit works because when it is closed the atoms flow from the battery through the wire through the lightbulb to turn it on.
Circuits go inside of things like a flashlight to turn them on.