The chord Bb/G# that is shown here contains the notes: Ab, D, F, Bb. The root of the chord is Bb (The lowest sound - the bass - is G#). The scale from which the chord is derived is Major, and the degrees of the scale are: 1, 3, 5.
To play the chord Bb/G# shown above, place your fingers as follows:
On string number 4 (the thickest), on fret number 1 with finger number 1 (index finger)
On string number 3, on fret number 2 with finger number 2 (middle finger)
On string number 2, on fret number 1 with finger number 1 (index finger)
On string number 1 (the thinnest), on fret number 1 with finger number 1 (index finger)
Finger numer 1 presses multiple strings as a barre.