This series is not so much a progressive course, but represents a selection of topics. However, looking at any video, topics of the videos with lower number need to be understood to make sense of it.
Here is the order of topics:
1) Names of keys 2) Tones and semitones/chromatic scale 3) Major scale 4) Minor scales 5) Major and Minor relatives
1) Names of keys
2) Tones and semitones/chromatic scale:
3) Major scale
4) Minor scales
5) Major and Minor relatives