Here is a short jazz theory lesson on seventh chords, and some relatives like ninth, sixth and 13th chords- Four-String Chord Voicings.
This is a lesson going over some of the common chord voicings guitarists, particularly jazz players use when accompanying a vocalist or just generally playing rhythm guitar. There are three main families - one each with the root on the 6th, 5th and 4th strings. It also goes into some 9th chords and other relatives.
