I saw a plane leaving Luton Airport that I have never seen before. It seemed to have an extra small rectangular wing near the front of the plane. What is it?
That would be a canard you see on the airplane.
An aircraft designer may adopt the canard configuration to reduce the main wing loading, to better control the main wing airflow, or to increase the aircraft’s maneuverability, especially at high angles of attack or during a stall
Canard foreplanes, whether used in a canard or three-surface configuration, have important consequences on the aircraft’s longitudinal equilibrium, static and dynamic stability characteristics.
Many pioneers initially followed the Wrights' lead. For example, the Santos-Dumont 14-bis aeroplane of 1906 had no "tail", but a box kite-like set of control surfaces in the front, pivoting on a universal joint on the fuselage's extreme nose, making it capable of incorporating both yaw and pitch control.
I hope this has helped.