Hi, I know the fingerings of the diatonic scales, but I don't know how to figure out what chords belong to what scales.

eg. A major scale, my question would be, what chords belong to that progression?

^I just skimmed that, but it doesn't appear to answer his question. The other, equally likely, scenario is that I'm an idiot.

Anyway, creating triad chords from a scale is easy. You take a note and, skipping every other note, play the next three notes. Here is an example. C D E F G A B C is a C major scale. The first chord is C, C E G. C D E F G A B C. Let's do the second chord, Dm, D F A. C D E F G A B C.

Do you see the pattern?