The Jab Step is used in basketball to allow the ball handler to read the defender and make next move accordingly.  The ball handler should hold the ball facing the defender.  The shoulders should be turned away with the ball being held on the back hip of the ball handler.  The player will step forward with their front foot and quickly step back (the gap step).   The back foot needs to be the pivot foot. 

Next move - The player will step forward if the defender does not move, then the ball handler will make next move to either the left or right and will drive past defender. If the defender does move, the ball handler will move in one direction and then cross-over toward the opposite direction.    The key is to read how the defender reacts to the gap step. Also this is performed after receiving the ball on a pass, and the player has not yet dribbled.