× = don't play that string, ○ = open string. Numbers next to a diagram give the fret it starts on.
See every A♭ note on the neckA♭ is one of the seven chords in: D♭ major (V), B♭ minor (♭VII), A♭ major (I), F minor (♭III), E♭ major (IV), C minor (♭VI).