Watch the Introduction Theory online guitar lesson by Matthieu Brandt from Chord Cookbook
This section contains a short rundown of the theory you need to understand where chords come from. The chords we'll discuss in the first sections are built on the notes of an Ionian major scale. Each chord tone functions as the root for a chord; major or minor. You can derive these chords from the Ionian major scale through the formula 1-3-5 for three note chords and 1-3-5-7 for four note chords.