balance
Sure, you can steer by using your sails. Ease the headsail to turn upwind; ease the main to turn downwind.But, assuming you're not sailing something huge, you may do better by moving crew weight around. The boat moves to the opposite side of the crew weight. So, to steer upwind, put the crew on the downhill side of the boat, and vice versa.Steering without using the rudder's not too hard (at least on my little 20 footer.) Tacking without a rudder is trickier. Letting the jib backwind in the middle of the tack helps a lot.