The Chords – C Major:  as the guitar has no flats of sharps on any open string we can observe the chart showing the key scale to see this will be a C major tuned instrument.  So in order for progressions C will be the first in this sequence.

The Chords – A Major: following C major is the second chord in this sequence, the A Major chord has “bar” capacity.  This means it can slide up and down the fret board in one position to achieve any other key via position of root finger.