When to use it: For a relaxed, but generally major key vibe. Over a I-IV-V progression (such as G-C-D) where the V chord is the root (D-C-G). Mixolydian is a versatile scale. Its sonic signature is ...
If you only ever learn one scale, then it has to be the major scale. If you know how this one works then you open the door to understanding how chords are built, what chord names mean, how scales and ...