A 2 channel plane is usually throttle and rudder control. The throttle will control the climb and descent of the plane. Give it more throttle to climb and vice versa. And the rudder controls your turning.

A 3 channel plane is usually throttle, rudder, and elevator. The throttle will control the speed here with the elevator controlling climbing and descending. And the same with the rudder, it will control your turning.

Ken