Slash chords just tell us what note to play in the bass. They’re usually pronounced as the chord name “over” the bass note. For example D7/F# we would say “D7 over F#” and it means play the F# as the lowest note.
D7 is quite a common one … play an open D7 chord like this
E |–2—-||
B |–1—-||
G |–2—-||
D |–0—-||
A |–X—-||
E |–X—-||
Now hook your thumb over and play the F# in the bass on the low E string.
E |–2—-||
B |–1—-||
G |–2—-||
D |–0—-||
A |–X—-||
E |–2—-||
That’s the basis of slash chords. Sometimes the note is not part of the chord, but often it is, which means we’re just playing an inversion.
Does that make sense?
So do we replace the root with the F# or we add the f# as the lowest note
Lowest note. For example C/G you could play the normal open C chord but also add the G on the sixth string third fret.
