The stick on the left side of your transmitter moves fore and aft for throttle, and, beleive it or not, it also moves left and right for rudder.

Rudder is used to yaw the airplane. You can get by without usng the rudder, bur your turns, especially at lower speeds will always look funny without it. Try holding a little rudder in the direction of the turn and watch what the tail does. You may have to neutralize or even put in opposite aileron to maintain your bank angle. I'm a big advocate of learning rudder inputs as you learn to fly rather than after you've learned to fly with Ail/Elev only.

Richard