I just figured out why certain keys (like Am) are the relative minor to a major key (like C). Go to a Piano and play only the white keys up and down starting at middle C. You've played a C major scale. (have someone show you where middle C is). Then move your finger to the left two white keys. Next white key to the left is B, skip the black key (Bb/A#) and the next white key is A. Now play a scale only on the white keys from this A up to the next A and back and you will be playing an Am scale. Same with Key of G. You have to sharp one note, the F to F# (instead of playing the F white key you move up to the black key, F#), and this gives you the same relationship of half steps to whole steps between notes so you get a G major scale playing all white keys on the piano except for the F which is now an F#. Now move down to the white key that is E (the relative minor to G major) and play the same scale as you did with the G major scale except start on E and end on E. You've played an E minor scale. That's why certain minor keys are the relative minor to certain major keys.