A jab is deliver from your front hand and a cross come from you rear hand. The cross uses the waste, and chest more. If you do a proper cross you should end up on the ball of you left foot, with the foot faceing the opponent.
I know you didn't ask this but heres a tip, do you know of the 80/20 rule.
Your front hand should be used for 80% of the offence, due to jabing, and setting up while the rear should be used for 20%, only on sure fire powerpunches.
While on defence the rear hand should be used 80% of the time to stop oncoming punches and the front hand should be used 20%.