The fire heats water in the boiler until it turns into steam.
Steam takes up lots of room, so it pushes the piston along the cylinder — that's the "PUSH" stroke. The flywheel carries it back on the "RETURN" stroke.
The piston turns the crank, spinning the heavy flywheel round and round.
The pressure gauge climbs as the boiler heats up, and the spinning governor balls fly outward when the engine runs fast.
More fire makes more steam — and a faster flywheel! Tap the engine to blow the steam whistle.