You ned to be conversant in the safety issues as well as learning to drive, get a few lessons a video may not tell you how to hitch up safely, one golden rule is NEVER let anyone sit in the cart by themselves, if the horse takes fright they have absolutely no chance of bringing a runaway cart under control again.
Hold the whip when learning otherwise you will simply never learn

ONce you have it you will not be able to drive without a whip, neither should you try, the whip should be there as an aid to your voice and to distract the horse if they get spooky.
Hold the reins in your left hand, pointy finger and middle finger separating them. Keep them faily straight, make sure the left rein is over the pointy finger and the right one between your middle and ring fingers. Grip the reins with your ring and little finger and your thumb should be horizontal lightly gripping the reins too. Keep your right (whip) hand up with your left ready to assist it, although you hold the reins in your left hand your right hand should be constantly making adjustments and ready to shorten the reins or take hold in an emergency.
To make small adjustments on a straight line...to go left roll your wrist towards you slightly to the right of your body, the left rein will shorten and the right rein will loosen. To go right drop your wrist, rolling your thumb away from you, the other rein will then shorten and the left rein will lengthen. If you need to turn tight use your right hand, never open your hand to the side, imagine working towards the centre of your body over your left hand.
If you want to see my two Haflinger Stallions in harness go to
www.geocities.com/tonkii2000/horses
Hope this helps a bit, but I would practice with the reins on the back of a chair, practice getting the chair to balance on two legs!