This example is another tasteful way of accompanying a minor blues. Magic Sam and Eric Clapton used these chord shapes in songs like “All your Love”.
What you’re doing is playing three note chords on the top three strings.
Each minor or major chord consists of a root, a third (major or minor) and a fifth.
Each of these notes can be played as the bass note, thus forming three different inversions.
A good example of this are the three different forms of the Am chord, played in bars 1, 7 and 11 of this example.
The bass notes are an A, an E and a C. The notes of an Am chord are A, C and E. So you see.
Playing these inversions in a steady rhythm makes for good accompaniment. Don’t alter the pattern you play too much; it’ll start to look like a solo.
You can also make inversions with 4-note chords.
The principle stays the same; alter the bass note and find the other notes of the chord higher up the strings.