How do I perform marching?

Lie on your back with your knees bent and feet flat on the floor. Toes are pointing forward and arms are by your sides in a position that is comfortable for you. Gently draw your abs in by pulling the area just underneath your belly button toward your spine. Slowly lift one foot off the floor (keeping the knee bent) as high as you can in a controlled manner. Hold the position for 1-2 seconds and then slowly return the foot to the floor. Repeat the movement on the other side. Continue alternating legs for the required number of repetitions.

Lie on your back with your knees bent, keep your feet flat on the floor and your toes pointing straight ahead.  Gently draw-in your navel towards your spine and contract your glutes.  Slowly lift one foot off the floor with control, hold in the air for a few seconds and lower your foot back to the floor.  Repeat with the other foot.