The Brainliest Answer!
Of more relevance to the guitar player are Chord Families, or the groupings of chords that go with the keys. Looking again at the C major scale, with the numbered notes we have:
1  2  3  4  5  6  7  8 
c  d  e  f   g  a  b  c
Each note can represent a specific chord in the key of C. For instance, the first note ‘C’ represents the first chord C (major). The fourth note ‘F’ represents the fourth chord F (major). Some of the numbered notes represent major chords, some minor, but the seventh represents a ‘diminished’ chord. Look at this chart of Chords for the Key of C:

I      ii       iii      iv     v      vi
c    Dm    Em    F     G     Am
3 4 3