CAGED is the basic theory of, all guitar chords more or less fall into five shapes, C A G E D. It is important to realize that while CAGED is not the only system for learning guitar, it is certainly a useful start. There is no magic finishing line, learning guitar takes a lifetime, hence guitarlife.org.
Here is an intro to CAGED as explained on YouTube.
This is interesting to say the least. Regardless, many songs are also played in those keys, either way, I will post more information here when I have access to it.
Quick Chords – Key of C
C, Dm, Em, F, G, Am, G/B
A, Bm, C#m, D, E, F#m, E/G#
Quick Chords – Key of G
G, Am, Bm, C, D, Em, D/F#
E, F#m, G#m, A, B, C#m, B/D#
Quick Chords – Key of D
D, Em, F#m, G, A, Bm, A/C#