The chord Abm/A that is shown here contains the notes: A, Eb, Ab, B. The root of the chord is Ab (The lowest sound - the bass - is A). The scale from which the chord is derived is Minor triad (1–♭3–5), and the degrees of the scale are: 1, ♭3, 5.
To play the chord Abm/A shown above, place your fingers as follows:
On string number 5, on fret number 0 (open string)
On string number 4, on fret number 1
On string number 3, on fret number 1
On string number 2, on fret number 0 (open string)
Start strumming from string number 5 (notice not to play strings 1 and 6).