There are several important words needed to describe an airplane's flight and how to contorl it. These terms apply primarily to real airplanes but are very useful when talking about paper airplanes as well.
Airplanes have many different movable surfaces which the pilot controls during flight. The flaps adjust wing area and increase lift for lower speed landings. Ailerons roll the plane to the left or right for sharp turns while a rudder swings the tail back and forth for gradual turns. In the tail section there are elevators to raise or lower the nose for climbing or descending.
The altitude of an airplane means how it is pointed with respect to level ground. There are three terms used to describe how an airplane moves from a normal attitude of flat and level to something different. The first is pitch a pointing up or down of the nose. Roll is a turning motion in which one wing tip rises while the other falls. Finally, yaw is a side to side motion of the plane.
Another important term used to describe the wings of a plane is dihedral angle. This is an up and down angle the wings make with the body. If an airplane's wings are completley flat, it will be less stable when flying and have a tendency to roll. Setting this angle is important when flying paper airplanes. Each plane has an ideal angle which is found by trial and error.