I recommend you listen to Episode #4 before diving into this bonus episode.
So you've learned to count "by two" through the musical alphabet: A, C, E, G, B, D, F. Now you can quickly name the notes in any one of those chords by leapfrogging; what are the notes in a C chord? c, e, g. The notes in an F chord? f, a, c. Awesome!
But if you listen closely, some of the chords you create will be major and others will be minor. Just remember: "I have an iDEA." That will remind you that the chords D, E and A need sharps in order to be major chords. For example the D major chord is d, f#, a. The E major chord is e, g#, b. The A major chord is a, c#, e. The outlier is the B chord which gets two sharps: b, d#, f#.
Why do we want to make every chord a major chord? Because most musicians use the major chord as their harmonic starting point. It's the "vanilla" of music. Start there, then add fancy toppings! When you can name the notes in any major chord you have a foundation from which to grow in your understanding of music.
Notes in major chords:
A: a, c#, e
B: b, d#, f#
C: c, e, g
D: d, f#, a
E: e, g#, b
F: f, a, c
G: g, b, d