There are seven modes, each named after a province in Greece. They are the Ionian (major), Dorian, Phrygian, Lydian, Mixolydian, Aeolian (minor), and Locrian. There is a simple formula to change the Ionian (major) scale into any of the other modes....
To Change Ionian Into Another Mode:
Dorian: flat the 3rd and 7th notes of Ionian a half step.
Phrygian: flat the 2nd, 3rd, 6th, and 7th note in Ionian a half step.
Lydian: sharp the 4th note of Ionian a half step.
Mixolydian: flat the 7th note of Ionian a half step.
Aeolian (minor): flat the 3rd, 6th and 7th notes of Ionian a half step.
Locrian: flat the 2nd, 3rd, 5th, 6th, and 7th notes of Ionian a half step.
Every major scale has a relative minor in it...just take the sixth note in the scale, and that is the relative minor of that scale. Simple, huh?
The relative minor of A major is F.
Relative minor for B is G.
Relative minor for C is A.
Relative minor for D is B.
Relative minor for E is C.
Relative minor for F is D.
Relative minor for G is E.
Natural minor is just a major scale (Ionian) with the 3rd, 6th and 7th notes flatted a half step (making it Aeolian). It is darker sounding, and works over a minor chord, minor 7th chord, or a power chord of the same name.