Semitones Or Half-Tones

In the first part, we say there are only 12 musical tones before the 13th tone repeats the first tone at one octave(cycle) higher.

These 12 musical tones are each a semitone/half tone apart from each other. (or 0.5 tone apart).

The guitar is a fretted instrument with each fret a semitone apart, sounding higher when moving towards body.
So if we start anywhere playing each note progressively higher up each fret (on same string), then after 12 consecutive notes, the 13th note will sound the same as the first but at one octave higher.

Finally, starting on the 2nd string 1st fret, instead of playing the 12+1 consecutive semitones, play this pattern of semitones of 7+1 notes:-

2nd String 1st Fret
1st | | 3rd | | 5th | 6th | | 8th