With the inclusion of sharps and flats, there are 12 different notes within one octave as shown in the following diagram
The notes EF and BC are always on semitone apart (1 fret). The other notes are a tone apart (2 frets). Sharps ( #) and flats ( b ) are found between the notes that are a tone apart:
This scale is called the chromatic scale and contains all the sharps #’s) and flats (b’s) possible. C sharp (C#) has the same position on the fretboard as D flat (Db). They are the same note but can have different names depending upon what key you are playing in. The same applies to D#/Eb, F#/Gb, G#/Ab and A# /Bb. These are called enharmonic notes. The diagrams that follow show all the notes on the guitar including these sharps and flats.
Also notice that:
These note positions are important to remember because they are the basis for tuning your guitar to itself (refer to the section on tuning the guitar to itself).