Since Pythagoras developed the musical scale (C D E F G A B C), it has been necessary in order to continue the evolution of music, to clarify, or to enlighten the path of musicians.
Music might look like a mystery just because of that lack of that simple and important true. And that simple true is that in every single major scale, there are intrinsically—its minor seven scale (and thus the chord), its major seven scale, its minor scale, and its diminished scale.
There are five figures or diagrams, which save hundreds of words and teach you how to master all the harmony scales and thus chords.
Enjoy, enjoy, and create your own music.