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