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