A sharp (#) raises the pitch of a note by one semi-tone (1 fret).
A flat (b) lowers the pitch of a note by one semi-tone.
In music notation the # and b signs (called accidentals) are always placed before the note.
This example illustrates that the same note has two different names (i.e., F# and Gb have the same position on the fretboard).
A natural (@) cancels the effect of a sharp or flat.
A sharp or flat, when placed before a note, affects the same note if it re-occurs in the remainder of that bar. It does not, however, affect notes in the next bar, e.g.:
With the inclusion of sharps and flats, there are 12 different notes with one octave, e.g.:
Note that there are no sharps of flats between B and C, and E and F.