Start with a C Major scale. The notes of this scale are
C D E F G A B C
No sharps or flats to get in the way here! I will show the notes on a piano keyboard like this -
As you can see, there are extra notes in between the C major scale notes.
These gaps determine how a Major scale sounds. The gaps between the scale look like this -
C (Gap) D (Gap) E (No gap) F (Gap) G (Gap) A (Gap) B (No Gap) C
To make it easier to read I will show a Gap as Number 1 and No Gap as 0 -
C 1 D 1 E 0 F 1 G 1 A 1 B 0 C
So the Major Scale gaps are 1 1 0 1 1 1 0
Playing this on the guitar is really easy. Start on C (A string/5th string, 3rd Fret)
Going up the fretboard, play the notes, leaving gaps in the right places.
This same scale shape can be used starting on any fret. Starting on fret 5 is the D major scale, starting on Fret 7 is the E major scale etc. To play a Major scale on the guitar you can use a variety of different scale shapes, as long as the gaps are kept the same ( 1 1 0 1 1 1 0 )
See and hear the C Major Scale played on the guitar in this video...