Watch the The Layout online guitar lesson by Annie Raines from Blues Harmonica Blueprint
The harmonica was designed to play chords as well as melodies. If you blow into the first hole of the harmonica and slide from left to right, you will play C major triads, repeating up the harmonica and ending at C on the 10th hole. When we draw from 1-10, we get a G chord on the first 4 holes: D-G-B-D. Moving up to the 5 hole, we get an F, which turns this G chord into a G7, the classic dominant 7th that dominates blues songs. The 6 draw is an A, extending the G chord to a jazzy G9 if you want it, or capping off a D minor triad. From 7-10 draw, the notes repeat: B-D-F-A.