To find the relative minor of any major key, start on the 6th degree of the major scale. This example shows the scale tone triads for the key of A minor, with the chords being derived from the natural minor scale. As you will see, the chords are exactly the same as those contained in the key of C major. The only difference is the starting and finishing point. Because the minor scale starts on A, A minor will now be chord 1 instead of 6. As with major keys, notice how the chords are constructed as two lines of 3rd intervals. These can instantly be used as harmonies in the key of A minor.
The following progression could be described as 6 1 5 6 4 5 6 1 5 4 5 6 in C major or as 1 3 7 1 6 7 1 3 7 6 7 1 in A minor. Because the progression has an obvious minor tonality (tonality), musicians would use the second description. Try Writing out the notes of this progression as S A T B voice parts.