Answer:
A "foot brake" is activated by pedalling backwards. They may overheat on very long descents, and poor, or poorly maintained ones can catch nastily.
They're often perfectly good for a low-maintenance, high reliability option on a utility bike used for casual riding.
To use one safely, first move your weight towards the back of the bike. This will put more weight over the rear wheel, making it less likely to start skidding.
Next, begin to back pedal slowly, until you feel the brake engage.
If you need harder braking, push harder on the pedal. Be ready to remove the weight from the pedal if the wheel should lock up.