If you build three note chords (root position triads) from each degree of a major scale in turn, the triads you will get will be
1 major,
2 minor,
3 minor,
4 major,
5 major,
6 minor,
7 diminished.
These are the basic chords used to harmonise a melody in a major key (D major in this case). The most commonly used of these chords are the three major chords at scale degrees 1, 4 and 5. Many simple tunes can be harmonised with just these 3 chords.
The distance between the top and bottom notes of a root position triad.
The distance between the top and bottom notes of a root position major or minor triad.
The distance between the top and bottom notes of a root position diminished triad.
The distance between the top and bottom notes of a root position augmented triad.
Take any note. Drop down a perfect fifth from that note. Continue doing this (sometimes jump up an octave to stay on the piano). You will cycle through all twelve notes before returning to where you started. The circle of fifths is the foundation of the vast majority of chord sequences in western music. Get to know it well! There will be plenty more on how to use it in future lessons.
The circle of fifths, keeping to the notes within a particular scale/key rather than always using a perfect fifth. This will cycle through all 7 notes in the scale.
Play the triads of a major scale up through the degrees of the scale 1 - 7.
Repeat, but this time with the triads in first inversion.
Now try second inversion.
Now try another scale.
Play the triads of a major scale through the diatonic circle of fifths.
The triads should go in this order: 1 (major), 4 (major), 7 (diminished), 3 (minor), 6 (minor), 2 (minor), 5 (major), 1 (back home).
Now play the same again, but this time vary the inversions you use to minimise how far your hand needs to move. For example, play 1 in root position, then 4 in second inversion, 7 in first, 3 in root, 6 in second etc.
Let's harmonise Twinkle Twinkle using the 1, 4 and 5 chords of a major scale. The start goes like this:
1, 1, 1, 1, 4, 4, 1, 4, 4, 1, 1, 5, 5, 1
Try playing the chords above in root position with your left hand, while your right plays the melody.
Next play the chords with your right hand instead, but change the inversions so the top note of the chord is the melody note. Once you get the hang of this, add the root note (the bottom note of the root position triad) of each chord underneath with your left hand.