In a biathlon event, competitors cross-country ski for a pre-determined distance, and then stop at a rifle range to fire at targets. In all events, the targets are 50 meters downrange. In some events, the skiing portion is truly cross-country. In others, skiers race around a course. After each lap around the course, they stop at the shooting range.
Shooting portions are conducted in either the prone or the standing (sometimes known as off-hand) positions. The athletes do not choose the position -- each event requires different shooting positions at specific points in the race. In the standing position, the target area is 11.5 centimeters in diameter. In the prone position, the target is only 4.5 cm wide [ref]. In addition, the wrist can't touch the ground while in the prone position.
At the firing range, each competitor has five targets, with one round of ammunition per target. In every event except individual, each missed target results in a 150 m penalty. The penalty includes skiing around a 150 m loop off to the side of the main course. In the individual event, each missed target adds a penalty of one minute to the competitor's final time.
The relay event differs slightly in that the athletes have three extra rounds at each firing range. They still have to strike five targets, but if they miss on any of the first five shots, they can load additional bullets to get the remaining targets. Loading a bullet takes five to seven seconds [ref]. Each target that remains standing after all eight shots have been fired results in a trip around the 150 m penalty loop.