Music theory describes the construction of different types of chords. A major chord consists of the 1st, 3rd, and 5th notes of the major scale, while a minor chord uses the flattened 3rd note. The difference between major and minor scales is that the minor scale uses the flattened 3rd, 6th, and 7th notes compared to the major scale. Various chord types are formed from different combinations of notes within scales, such as major seventh, minor seventh, dominant seventh, and suspended chords.