Basics
Scale formulas
The major and minor scales as step patterns — the ruler every chord is measured against.
A scale is a sequence of whole steps (a tone, 2 frets) and half steps (a semitone, 1 fret). The major scale is T–T–½–T–T–T–½. Play it from C and you land on the white keys.
The natural minor scale is T–½–T–T–½–T–T. From A it uses the very same notes as C major, just started on A — that's why A minor is the relative minor of C major.
Chords come straight out of the scale: stack thirds on each degree and you get the chords that belong to the key — the tonic minor (Am), the dominant (E7), and the rest.
Manouche also leans on the harmonic minor: raise the 7th degree a half step. That raised note (the leading tone) is exactly what makes the dominant pull back home.