Your bones in the hands are called the “phalanges” and surrounding them are your skeletal muscle, it’s the muscle that lines the skeleton and the joints and muscles in your arm, wrist and fingers all work together. When a person makes a fist the muscle in the fingers and palm flex and the bones and joints all make the “ fist” movement possible. And to relax the fist the muscles contact with the joints and become limp.
I hope this helped