Sounds like you have a broken or stripped servo. I would consider replacing it with another 9gram servo if you can get your hands on it.
Did this happen after a crash? or just after purchasing the plane? If it's new, then you need to first center the trims, little push buttons on your transmitter radio. Then you pop open the clevis from the control horn, screw it in or out to change the length of the control rod, and reinstall it.
About the names of stuff, it's like this: The "Servo" is the little box thingy in the wing. The "Control Arm" is the nylon thingy on the servo going to the metallic "Control Rod". The other end of the control rod has a "Clevis" screwed on. This is to adjust the length of the control rod. The Clevis is popped onto a "Control Horn" which is in turn glued to the "Aileron".
Make sure it's working smoothly before flying. If it locks up you could have a bad gear in the servo which could make you crash.