The image above shows the starting position for this exercise. Your knees should be more or less directly under your pelvis and your elbows directly under your knees. If you find this position uncomfortable, you can try resting on your hands, rather than your elbows.
When you are ready, raise one leg directly upward as high as you can without arching your back, keeping the leg either straight or slightly bent. Then hold the leg in that position and don’t let it drop (if you can) for 15 seconds. Then bring the leg down and back into the original position before repeating the exercise on the other leg. Do this 5 times on each side, once a day.