You sit in the seat, here, and put your feet here, on the petals. When you move your feet, in a circle like this . . . that turns the wheel.
Because of the gears, each turn goes a long way, so you can probably go pretty fast. To stop, you pull the levers here and here toward you — that puts the claws against the ground, slowing you down. They're your breaks. And the harder you pull, the faster you'll stop.