A minor chord is a basic triad made of the root, a minor third and a perfect fifth. Am, for example, is built from A, C and E.
The basic idea
Compared with a major chord, the third is a semitone lower, and that one difference changes the impression greatly.
What to check when using it
Play major and minor alternately on the same root and hear the difference in the third for yourself.
Do not assume minor chords are simply dark; use them together with tempo, timbre and progression.
