The aileron is the hinged part of the trailing back edge of the aero plane wing. It is responsible for how much the aircraft rolls on its longitudinal axis. That is how much the aircraft rolls in midair. The pilot needs to learn the configurations of the different aileron positions in order to make the desired turn.
This becomes second nature with practice. For instance, when you shift the plane to the right, the right should be up and the left aileron trailing edge should be down. This allows the plane to make a right turn. Knowing these different steps and positions is important for the pilot.