The basic chords of music are TRIADS – 3-note chords composed of various intervals of the scale based on the root, 3rd, and 5th and their alterations. To form a 4-note chord you simply add a note of the scale such as the 6th, 7th, or major 7th to the basic triad. This short video demonstrates how this works:

For a COMPLETE course in chords click on “All The Chords In The Whole Wide World!”