Tetrad chords (aka four-note chords) represent the backbone of jazz harmony. It is common to extend them with extra tones. These other notes form the upper structure of a chord which includes the 9th, 11th and 13th.
Adding extensions to chords help to get off the beaten tracks and provides some new harmonic colors to your playing (chord soloing, comping, and arrangement).
This lesson provides useful extended major 7th chord shapes to apply to your playing.