The way that you pronounce this chord is either "D
slash F sharp" or "D with a F sharp in the bass".
The letter to the left of the slash
is the name of the chord, so this is a D chord.
The letter you see to the right
of the slash is the bass note, or lowest sounding note of
the chord. Normally in a D chord the lowest sounding note
is D. But in a D/F chord, the lowest sounding note is a F (F sharp).