Lets look at Cm. Cm is made up of 1 b3 5. So that is C Eb G. So any scale with those notes in can be played over the chord.

But, I hear you shout, Eb Major, Ab major, Bb major all contain these notes, and surely you cant play Ab major over Cm?!

Well you can! because Ab major consists of Ab Bb C Db Eb F G. And by rearranging the scale and starting with the note C, we get C Phrygian! which is a minor mode! Bb gives us C Dorian, and Eb gives us C Aeolian.

So lets say we want to create a chord progression which allows us to stay in the key of Cm, or C Aeolian. That means we can use all of the chords which can be made up from the scale of Eb. Observe-

I-Eb, Ebmaj7, EbMaj9

II-Fm7, Fm9

III- Gm7

IV- Abmaj7, Abmaj9, AbMaj7#11

V- Bb7, Bb9, Bb11, Bb13.

VI- Cm7, Cm9, Cm11

VII- Ddim.

Now all these chords work with Cm. Why? Because Cm is the relative minor of Eb. That basically means Eb is C Minor!! But this is where it get interesting- if you play C minor over these chords, the notes may stay the same but the sound will change. C minor will sound happy over Eb, jazzy over Fm7, Dark over Gm7 etc! Its because technically speaking the Cm morphs into Eb Ionian, F Dorian, G phrygian etc! Same notes, different sound. And thats the secret of chords and modes- you can play the same notes over different chords and get vastly different sounds!

This theory can be used with any mode- find what the parent scale is. By that I mean E Aeolian is the 6th mode of G major, and then using a book, or whatever, work out all the chords you can get from the modes of G major.

For the reverse, to find out what scales to use over chords, simply write out the notes of the chord, superimpose them onto the Key's major scale, see what formula you get, and that will give you the scale or mode. Confused? Well, using Cm again, we have the notes

C Eb G

and the C major scale has-

C D E F G A B.

Which means the chord contains the formula 1 b3 5. Now any C mode with this formula can be used over the chord.

Hope that all makes sense!