The 9th Chord is frequently used in styles like funk and jazz. The chord is constructed by adding the ninth note in the scale to a dominant chord. The C9 for example, includes the following notes: C, E, G, Bb and D.
None for the moment in this category
As shown in the diagrams the 9th chords are movable and therefore really simple to memorize. To play the chord you have to lay your ring finger over the three highest strings (see picture to the right).
If you know how to play a 12 Bar Blues chord progression you can mix it up by replacing the IV7 and V7 with IV9 and V9. In other words, a 12 Bar Blues progression could look something like:
A7 – D9 – A7 – E9 – D9 – A.