Used together, the yellow ‘wheel’ pictured below, a 12 sided and segmented dedecagon with the note names and key signs imprinted on it, can be used in learning where on a 6 string guitar fret board each individual note is sounded.
With a guitar in standard tuning, lowest to highest, (heaviest to lightest, thickest to thinnest) strings tuned E A D G B E. One need only to determine where on the fret board an E is found to determine which note is above or below it.
Using the top left most circle on the fret board diagram as an E note, this would be an open string, no finger on the fret board is necessary to make the E note sound. The next note on the wheel moving clockwise is an F. This would correspond to the next circle just below the E note already referenced and be called the F note. One finger would press on the string just above the horizontal line representing the first fret of the fret board to make that F note sound.
And so on sequentially until at the 12th fret where the notes repeat but are and octave higher.
The next note is interesting in that it has 2 names. F sharp or G flat. That is, it can be written either way depending on the key signature seen below the note names on the ‘wheel’. This is known as ‘enharmonic’ written differently sounds the same, This happens with words sometimes. As an example the english words, two, to and too! All sound the same but are written differently. So the next circle below the E and F can be either F# or Gb the # and b being used to designate :