These so-called "slash chords" are inversions.
Yes and no.
Not all "slash chords" are inversions. There are non-inversion slash chords.
G/B is an inversion, since the bass note B is in the G chord triad.
D/E is a non-inversion slash chord since the bass note E is nowhere in the D chord triad.
The way to read them: chord first/bass note second
btw: the proper name for those chords is compound chords, while the popular name is slash chords.