The natural minor! The harmonic minor! The melodic minor! Like, why do we even have them?

This lesson isn't too hard, but you'll need to know what intervals are (like whole step, half step, etc.) and you'll need to have a basic idea of what a scale is.

Here's a good start on intervals and basic note relationships:    • How Basic Chords Work - Music Theory ...  
Here's a basic intro to major and minor scales:    • Major and Minor Keys (Music Theory)  

These aren't strictly necessary, but can be helpful:

Turning scales into chords:    • How to Fit Chords Into a Key (Music T...  
Introduction to modes (why the minor scale comes from the major scale):    • How to Turn a Mode Into Music  

00:30 Natural Minor
03:55 Harmonic Minor
11:02 Melodic Minor
14:14 Cat