Barre chord
fret 3, E shape355333
Gm is the G minor chord. Its notes are G, B♭ and D. The lowered third gives this triad its darker color.
355333
x-10-12-12-11-10
Numbers show frets from the low E string to the high e string; x means don't play that string.
Gm is the ii chord in F major, the iii chord in E♭ major and the vi chord in B♭ major. That makes it a natural fit in songs written in those keys.
Every G, B♭ and D on the first 12 frets. The filled dots are the root, G. Build your own shape from any nearby group.
Other G chords
Other minor chords