Start scene, wait for the world to come up, then drag inside the pad to move the selected arm's hand. Up/down on the pad reaches the arm forward/back, left/right moves it sideways; the z slider raises/lowers it. Motion is clamped to the arm's reach.

Move your hand in front of the camera; its wrist drives the selected arm — left/right and up/down mimic your hand, moving your hand nearer/further reaches the arm forward/back, and pinch your fingers to close the gripper (open hand = open). The camera overrides the pad while it runs.