D/F♯ Piano Chord
D/F♯ is a D Major chord played over a F♯ bass note. Because F♯ is the 3rd of D Major, D/F♯ is simply D Major in 1st inversion, the same notes with the 3rd moved to the bottom.
The dark key is the bass note (F♯); the coloured keys are the D Major chord tones.
Notes in D/F♯
Low to high: F♯ (bass) , then D – F♯ – A.
How to play D/F♯
Play the bass note F♯ low in your left hand, and the D Major chord (D – F♯ – A) in your right. Because it's an inversion, the bass is already one of the chord tones: you're just voicing D Major with its 3rd on the bottom.