To perform a wall sit, start by leaning against a wall with your feet about hip-width apart and your back flat against the wall. Lower your body by bending your knees until they are at a 90-degree angle, keeping your back against the wall and your thighs parallel to the floor. Place your hands on your thighs for support, using them to assist in holding the position, which helps to build strength and endurance in the lower body muscles, particularly the quadriceps.