To catch a ball below your shoulder, you take both hands and form a sort of bowl with them. So have them wide open to enable the ball to enter in the hands. As soon as the ball comes into the “bowl” formed with the hands, close the hands so the ball can’t jump out.
To take pressure of the ball, move the hands towards the body in the catching movement. This way the ball won’t just hit the hands, which really hurts, but goes smooth into the hands. Therefore it is important to bring them somehow back, in the catching movement.
As a cricket ball is quite hard and comes very fast, one need to be very careful while catching the ball and it can really hurt if something goes wrong and one can easily break a finger.