A rotary engine works by having the main internal components spin, as opposed to pushing up and down, to power your car.
A conventional engine has pistons that move up and down, similar to how your legs move on a stationary exercise bike. The pistons are attached to a crankshaft, which converts the up and down motion into energy that moves your car.
A rotary engine swaps the up and down pistons for ones that move in a circular motion, a more simple and efficient way to transfer energy to your wheels. This makes them much smaller, but don’t be fooled by their compact size. They’re actually quite powerful, and can even be scaled up to fit in larger vehicles.