Watch the Building Major Chord Triads online guitar lesson by Rob Garland from Chord Navigator: CAGED Triads

Major chords are built from the root, 3rd, and 5th of the major scale. If you take the note C as your root note, the 3rd note of the scale is an E and the 5th is a G. Play these three notes together and you have a C major triad. Note that when you play an open C chord you're stacking several of the same notes.