The natural minor scale is built from the 6th degree of the major scale. The natural minor is referred to as the relative minor of the major scale from which it is derived. So the relative minor of C major is A minor. Likewise, the relative major of A minor is C major.
The natural minor scale contains the same notes as the major scale from which it is built. The 6th degree of the C major scale is A, so this is the A natural minor scale:
Notice that the minor 2nd intervals are between the 2nd and 3rd degrees of the scale (B-C), and the 5th and 6th degrees of the scale (E-F). Also notice that the structure of the natural minor scale is the same as the major scale with 3 important differences: the 3rd, 5th and 6th degrees of the scale are all flatted. In other words they are each a half step lower than in the major scale.
It is common for a piece of music to shift from a major scale to it’s relative minor. If you have been playing for any length of time you have surely moved from a C major chord to an A minor, or a G major chord to an E minor.
It is also important to understand the parallel minor of each major scale. The parallel minor is the natural minor scale built from the root of a major scale. So the parallel minor of C major is C minor.
To create the parallel minor begin with a major scale and flat the 3rd, 6th, and 7th degrees of the scale:
Write the major scale, its relative minor, and its parallel minor, in all 12 keys around the circle of 4ths.
Learn the Natural Minor Scale on your guitar! Here it is in the key of G: