To analyze a chord all you have to do is look at what notes are in the chord. Take an A minor chord, which contains the notes A, C, and E. To find what scales will work over this chord, just look for scales with the root "A" and that contain the notes C and E. Three easy examples would be A minor, A harmonic minor, and A melodic minor. It's the same thing with modes, but it even works if you try modes with the root C or E (other than A). As you can see a simple chord like a minor chord is going to contain a very large number of usable scales. As you use more complex chords, that number will diminish even with just 7 chords. The best thing to do is to learn as many scales as you can and how they sound so you'll be able to choose the right one.