Mae-Geri-Keage (Front snap kick): There are two basic types of kick, keage (snap) and kekomi (thrust). This kick uses a snapping action from the knee, with your ball of the foot as your striking surface.
As a small tip on how to position your foot, if your place your foot flat on the floor, then raise your heel, but keep the ball and toes on the floor. Then, and keeping the same position you raise your foot from the floor; this will hopefully be the correct position.
This kick gets a little more complicated when you involve the action of the hips, but for a basic understanding of the kick, use this as a basic guide.

Stage 1: Raise your knee in front of you, keeping your back straight.

Stage 2: Begin to snap the kick outward from the knee

Stage 3: Be sure to keep the toes of the kicking foot retracted as the kick is completed.

Stage 4: Return the foot, again using the knee as the hinge.