The Natural Minor Scale
AKA Aeolian Mode

If you take the notes from A to A (no sharps, no flats)....this is an A natural minor scale.

A Natural Minor - A B C D E F G A

So an A minor scale is the 6th "mode" build from a C major scale. This idea is central to understanding modes. The major and the minor scales also have "modal" names. The major scale is also known as the Ionian mode, and the minor scale is also called the Aeolian mode. It is just another name for the same scale. But using the "modal name" usually indicates those same notes will be used in a little different way than you might have used them in the context of playing in a major key or minor key.

C D E F G A B C - C major (Ionian Mode)
1 2 3 4 5 6 7 1 2 3 4 5 6
          A B C D E F G A - A minor (Aeolian Mode)

If you compare A minor, to an A major scale, you can see that A minor has b3 (flat 3), b6, and b7 in comparison. This just means that "b3" is a half step lower than the 3rd note in the major scale.

A  B  C# D  E  F# G# A - A Major (Ionian Mode)
1  2  3  4  5  6  7  1 

A  B  C  D  E  F  G  A - A Minor (Aeolian Mode)
1  2 b3  4  5 b6 b7  1 

These numbers make up the formula for the minor scale. The formula for a minor scale is 1 2 b3 4 5 b6 b7. This is key to understanding modes. This is the way that you are going to compare what is the same, and what is different between different modes.

Page 1, Review of the major scale

Page 3, Relative modes