Every aircraft, from a paper plane to a jet, is governed by four forces: lift, weight, thrust, and drag. Understanding how they balance is the fastest way to become a better pilot and builder.
Lift is generated by the wings as air moves over them. Weight pulls the aircraft down. Thrust from the motor moves it forward, and drag resists that motion. A stable plane keeps these forces in balance.
When you set up your first RC plane, focus on the centre of gravity. A nose-heavy plane is more stable but harder to climb; a tail-heavy plane is twitchy and hard to control. Start slightly nose-heavy while learning.