Each fret and each string of the guitar represents a note. Some notes sound exactly the same but have two different names. This is called enharmonic. More on that later.
When we refer to all the notes on the guitar ,we are referring to the chromatic notes.
Chromatic Notes: Simply means all the notes on the instrument.
When we refer to natural notes we a referring to specific notes on the guitar.
Natural Notes : Are specific notes on the guitar.
Some notes have a symbol next to them to let us know if a note is sharp or flat, these symbols are call accidentals and tell us if a note is to be raised in pitch or lowered in pitch.
Accidentals : symbols that tell us to raise a pitch or lower a pitch
Sharps; (#) this symbol tells us to raise a note in pitch
Flats: (b) this symbol tells us to lower a pitch
Some notes have the same pitch but different names this is called enharmonic.
Enharmonic: Notes that sound the same but have different names.
Chromatic notes on the low E string
Ex 1: G# and Ab are enharmonic they sound the same but have two different names.
If you understand this information head over to Learning The Natural Notes Pt 3.