Hand locks are used as aids to get into certain positions on the silks which keep your hands in the same position throughout.
Keep in mind that hand locks are not meant to be bear your full weight. Their role is to help you stay up on the silks using your hands, but they will slip down if too much weight is loaded onto them.
Wrap your arm around one of the fabrics, starting with your arm on the outside of the silk. End with your hand open, not grabbing the silk.
Grab the tail of the silk and loop it over your wrist from the thumb side to the pinky side.
Now you have a hand lock! Repeat on the other side to make a pair.