× = don't play that string, ○ = open string. Numbers next to a diagram give the fret it starts on.
See every B♭m7 note on the neckB♭m7 is one of the seven chords in: F♯ major (iii7), D♯ minor (v7), D♭ major (vi7), B♭ minor (i7), A♭ major (ii7), F minor (iv7).