What pieces of the puzzle am I missing?

From any major scale there are three different relative minors. You can use any one (or more than one).

Sorry for the delay.... I just got back from running around the yard screaming, "FINALLY" multiple times. I'm starting to think I CAN get the hang of this.

I keep second guessing myself and the result leads to mass confusion and massive self doubt.

Thanks for sticking with me. Now I have to go and write this all down.

There are actually articles here. especially the ones by David Hodge, that explain this matter of the minors very well indeed.

Especially this one:Minor Progress.

Anyway, let's look at this for a moment.

If we build a scale straight from the major scale (1_2_34_5_6_78), we get the Natural minor scale (6_78_2_34_5_6 or 1_2b3_4_5b6_b7_8) with all the same notes. For example, C major (C_D_EF_G_A_BC) and A natural minor (A_BC_D_EF_G_A) have all the same notes. This scale is also known as the Aeolian Mode if you're into such arcana. "Losing My Religion" by REM is a good example of a song in A natural minor, as are many old folky songs.

So why complicate things? What is this harmonic/melodic doohickey of which we speak?

Well, major key music is all built on starting quietly on the I, building tension and excitement on the IV or ii, raising excitement and tension to a crescendo on the V or V7, then releasing the tension and going back to sweetness and light on the I.

So? So, the problem with natural minor is that the minor v chord doesn't have a lot of tension. It's dull, staid, even boring. Making it a minor 7th doesn't help. A minor 7th sounds even sweeter and more stable than an ordinary minor. What to do? Why not simply use a major V or even a dominant 7th on the V? Raise the 7th note (G -> G# in the key of Am) and our dull Em v becomes an E7, all aquiver with tension and pentup aggression, beautifully released by going back to the Am. This scale with the raised 7th is called the harmonic minor scale 1_2b3_4_5b6__78).

So far so good. But let's say we use the harmonic minor exclusively. This has some nasty side effects. Instead of a nice sounding G major on the VII and a C major on the III, we get a G#dim (G#-B-D) on the #vii and a rather ghastly sounding Caug (C-E-G#) on the III.

No problem, we just mix the two scales if we like and use the chords G and C on the VII and III and keep the E7 for the V.

Now there is still one minor problem in that our scale has a wide gap between the b6 and the maj7. A gap that sounded nasty in the old days and still sounds a little Arabic and exotic to us (try it). So to fill that gap, people often raised the 6th as well on the way up, giving the melodic minor scale (1_2b3_4_5_6_78) which can be treated much like a major scale with a b3.

I hope this helps.