What you are calling flaps are actually the Ailerons. The aileron servos plug into a Y harness and the Y plugs into the RX. The ailerons is what makes the plane bank. Most models do not use rudder to turn. A Cub will make a smoother turn if you use rudder and aileron together. It is not needed but will make a more scale turn.
Please don't take this the wrong way but you need a lot of help. You really need someone local to help you and show you how it is done. I could talk you through it but if you try and fly it by yourself it will crash. Not maybe crash but will crash.

David