To answer Ed...
No, the vang and traveller are not really the same thing.The best way to see how this all works is to go out on a medium wind day with a decently steady breeze. Center the traveler, and then sight up your sail looking at the alignment of the top batten with the boom (the "twist" in the main). Now drop the traveler and sight up it again. Now ease the vang and look up again. Etc, etc... Keep tweaking with it to see the effect of each.The general rule of thumb is to keep the top batten parallel with the boom, and the sail as full or flat as conditions dictate, with your leach telltales streaming cleanly.The mainsheet does not provide control over the twist of the sail. The combination of sheet, vang, traveller, outhaul, downhaul, and halyard give you that control.Now, with all of this said - for just bombing around and sipping a cool one, you don't have to worry about most of this!- AndyS