The chord B/C# that is shown here contains the notes: C#, F#, B, A#. The root of the chord is B (The lowest sound - the bass - is C#). The scale from which the chord is derived is Major, and the degrees of the scale are: 1, 3, 5.
To play the chord B/C# shown above, place your fingers as follows:
On string number 4 (the thickest), on fret number 6
On string number 3, on fret number 6
On string number 2, on fret number 7
On string number 1 (the thinnest), on fret number 6