Like the Roundhouse kick, the Side kick requires full rotation of the hip, pivoting of the foot remaining on the ground, and it can also be executed with either the front or back leg when in offensive or defensive stance.
When kicking from offensive stance with the back leg, the right leg (trailing leg) is bent, and the knee raised into the same chambered position as in the roundhouse kick. At the same time, the left foot will pivot until its heel is facing the direction of the kick - 180°. The leg is then extended straight out, and the striking surface is the side of the foot and heel. It is important not to let the knee dip while extending the kick - this will cause damage to your knees! Keeping the knee raised high when chambering the kick will generally ensure that the knee won't dip when you extend the kick. The kicking leg should be rechambered fully before returning to stance. It is also important to avoid "snapping" this kick - maintain full leg extension for at least a second before rechambering and returning to stance.