Turn the crank. Follow the chain, rear sprocket and wheel.
Tap the pedal. Watch the back wheel.
Wheel turns per crank turn: 2
What happens
The chainring moves the chain, which turns the selected rear sprocket. During forward pedalling with the freehub engaged, the rear wheel turns with it.
Here the chainring has 32 teeth. With 16 teeth at the back, one crank turn produces two wheel turns; with 32 at the back, it produces one. A larger rear sprocket gives a lower ratio.
A simplified illustration, not an exact model of your equipment.