On your two-handed backhand, put your dominant hand on the bottom of the handle and place the base knuckle of your index finger on the upper right bevel. Your non-dominant hand goes on top, with the base knuckle of your index finger ending up on the side panel. This is an Eastern forehand grip. The weight transfer, backswing, and finish are much like the onehanded backhand. The footwork is similar, but, because the player's reach is more limited on the two-handed backhand, the footwork must be quicker.
Most players can hit more topspin with the two-handed backhand.
Slice is more difficult with the two-handed backhand. Watch the whole stroke, observing the phases you observed for the one-handed backhand. Feel how it is different from the one-handed backhand. Determine which seems more comfortable to you. You must have QuickTime to view this file.