What the heck is an aileron? It’s a wing controller. It is a movable part of the trailing (rear) edge of the wing that can be moved up or down. Why? As you’ve learned, airflow over the wing surfaces gives the aircraft lift. By changing the shape of the wing with the aileron you can change the wing lift.
Why would you want to change the wing lift? To bank (tilt the wings left or right) and turn the airplane. Changing the wing’s shape increases or reduces lift. The aileron is efficient because it turns up on one wing to reduce lift and turns down on the other wing to increase lift. The result is that the wings bank and the plane turns in the direction of the lower wing.
The ailerons are controlled by the yoke, a flight controller that looks like half of a steering wheel. (Many planes have a joystick instead of a yoke, but they do the same thing.) Moving the yoke or stick to the left dips the left wing into a bank, and rolling the yoke or stick to the right dips the right wing into a bank. It’s a very important flight control and I’ll tell you more as we go along.
You might see a second wing controller on the trailing edge of the wings, inboard or closer to the cockpit. These are called the flaps. They only go down. Their function is to simultaneously increase the lift and increase the drag of the wing. Why? It lets the airplane fly slower—a very important function when attempting to land an airplane. Flaps are controlled by the pilot and can be set to various angles. Some aircraft combine the ailerons with flaps in what are called flaperons.
"Man cannot discover new oceans unless he has the courage to lose sight of the shore."
-- Andre Gide