There are three types of minor scales, which include Natural Minor, Harmonic Minor, and Melodic Minor, the latter being a unique variation of the minor scale. Natural Minor is one of the easiest minor scales to master in my opinion because they have relative majors, which means that they have the same set of notes but their tonics are different. For example, A Natural Minor and C Major are relative; they contain the same set of notes but start on different tonics. You can also learn how many whole-steps and half-steps major and minor scales contain to help you memorize these differences. Natural Minor is most commonly used in the electronic music scene.
Harmonic Minor varies slightly from Natural Minor. This difference lies in the last note of each scale before completing an octave; Natural Minor contains a sub-tonic and Harmonic Minor contains a leading tone. To help you understand this, look at Major scales. In C Major, B is considered to be a leading tone because it leads into C and is a half-step away from completing an octave. On the other hand, with A Natural Minor (also known as Aeolian), G is considered a sub-tonic because it is a whole-step away from completing an octave and doesn't necessarily lead into A. Harmonic Minor has a leading tone, and the simplest way to obtain a Harmonic Minor scale is to raise the seventh note a half-step and make it a leading tone. A Harmonic Minor differs from A Natural Minor because it doesn't contain the sub-tonic known as G, but it contains the leading tone known as G#, which is a half-step away from A. With any Natural Minor scale, raising the 7th a half-step makes it Harmonic Minor.
In musical notation, when writing out a Major scale, there are various methods to obtaining the Natural Minor and Harmonic Minor scales. If you were to write out a Major Scale, to obtain Natural Minor you would lower the 3rd, 6th, and 7th a half step. Lets look at A Major. It contains the notes A, B, C#, D, E, F#, and G (not including the octave). In this case, the 3rd, 6th, and 7th notes are C#, F#, and G#. If you were to lower each one a half-step, you would get A, B, C, D, E, F, and G, which is the A Natural Minor scale. The same method can be used for Harmonic Minor, which differs in which you do not lower the 7th. Back to A Major, the 3rd and 6th are C# and F#. By lowering just these, we get A, B, C, D, E, F, and G#, which is the A Harmonic Minor scale. This method can be used on any Major Scale.
Melodic Minor is the last, and it is a unique one. The above paragraph will most likely be helpful in determining how this scale works. Those that haven't studied music theory probably don't know why this one is special, so I'll lay it out. When writing it out in musical notation, it ascends an octave (as usual) but then descends to the 6th. If you are a bit confused by this, I'll clear it up in a bit. When it comes to Melodic Minor, you would only lower the 3rd WHEN ASCENDING (take note of ASCENDING), and so with A Major to A Melodic Minor, it would be A, B, C, D, E, F#, and G#. But wait, we're not done yet. When descending to the 6th, one must notate that the 6th and 7th are lowered a half-step, which makes F# and G# now F and G. In the A Melodic Minor scale, you have the notes A, B, C, D, E, F#, G#, A (including the octave), G, and F. Melodic Minor gives you access to a couple more notes to create some interesting melodies, but it should be noted that it's best to only use the lowered 6th and 7th when descending in a melody. For example, if you were going up from A, it's best to use F# and G#, but if you were descending from A, it's best to use F and G. It's not required, but is very much recommended.
Diatonic scales contain seven different tones, whereas Pentatonic contains five. The Pentatonic scale is not considered a minor scale because there can be both a Pentatonic Major and Minor. I hope that clears things up. Harmonic Minor sounds much more true to a "minor" scale because it sounds a lot darker. Just by playing the scale out you can tell the tremendous difference. Good luck
