Intervals 2nds, 3rd etc

Iiiinnn these videos - Intervals (not something in the middle of a show).......

Harmony keywords

diatonic      chromatic
consonant         dissonant
pedal        drone
cadences: perfect plagal imperfect interrupted
Tièrce de Picardie
identification of major minor and dominant seventh chords using Roman numerals/chord symbols

What is a chord

This may be helpful understanding what a chord is.

Cadences

If you are unsure about cadences, a basic but informative video to help.
Perfect, Plagal, Interrupted, Imperfect are the keywords.