There are some outstanding lessons here on WholeNote about the CAGED system. (See references at the end of this lesson.) While I have little to add to what the other instructors have so expertly said, I did find that having a handy reference chart can be helpful. With that in mind, here's a quick reference for 5 positions for each of the basic chords in the CAGED System. Following are the basic positions for each of the chords we'll be looking at.
Movable Chord Shapes