This first lesson introduces the first voicing group for the 12-bar blues in D on the middle group of strings. Let us call this Group A voicings. There are 2 chord shapes you must learn. The first chord shape is for the I7 chord (i.e. D7). The IV and V chords (i.e. G7 and A7) use the same chord shape albeit on different frets. Simply slide this shape to the appropriate fret position to get the desired chord.