7th chords, 9th chords, 11th chords ect.

(I will specify on 7th chords but the chords can be changed into 11th chords and 9th chords and such by changing the interval.

There are 3 different types of 7th chords. There is the 7th chord, major 7th chord and the minor 7th chord.

A 7th chord is made up of a major chord and a minor 7th.
So to make an E major chord into an E7th you have to find the minor 7th of the root note (E) which would be a D. The D note in the E major chord would be on the 3rd fret of the B string, which in an E chord is usually an open string.


A Major 7th chord is made up of a major chord and a major 7th.
To make an E major chord into an EM7, you have you take the major 7th of the root note (E) which is a D# and put that into the E chord. The D# note is on the first fret of the D string.


A Minor 7th chord is made up of a minor chord and a minor 7th.
To make an E minor chord into an Em7, you have to take the minor 7th of the root note (E) which is a D and put that into the Em chord. There is a D note on the 3 fret of the B string, which in an Em chord would be an open string.


Pictures from:
http://www.jguitar.com/