A unicycle is one of the simplest wheeled vehicles, consisting of little more than a wheel, a pair of pedals and a seat. Most unicycles do not have any sort of brake system installed on them, since the pedals are connected directly to the axle and are used to control the wheel directly. Being able to stop a unicycle when it is moving is an important skill, however, and is relatively easy to do provided that you are familiar enough with riding a unicycle to keep your balance while braking. Being able to brake effectively may take some practice, but the action of braking is in itself very simple.
Stop actively pedaling forward, allowing the unicycle to coast for a moment while your feet remain on the pedals. Don't try to stop the pedals from moving while coasting.
Lean forward slightly and reverse the direction of your pedaling. Don't make a full revolution with the pedals; you don't want to go backwards. Apply just enough backwards pressure on the pedals to stop your forward momentum.
Pedal your feet slightly back and forth, moving your upper body slightly in the opposite direction of your pedaling so that you can keep your balance while remaining stationary. You may also put one or both feet on the ground once the unicycle has stopped if you don't wish to idle on the cycle.