× = don't play that string, ○ = open string. Numbers next to a diagram give the fret it starts on.
See every B♭m note on the neckB♭m is one of the seven chords in: F♯ major (iii), D♯ minor (v), D♭ major (vi), B♭ minor (i), A♭ major (ii), F minor (iv).