Say we're in the key of C major. Say you want to know what chords are in A Minor. Well you already know the major one:
Maj Min Min Maj Maj Min Dim
- now start on the sixth chord, the Minor, which will be your A minor, and start counting from that. So it would be like:
Min Dim Maj Min Min Maj Maj
get it? Of course this can be applied to of the modes.
As for something like harmonic minor, well the rule is that the fifth chord is going to turn from a minor to a major. So in the key of A harmonic minor, you're going to have an E major chord, as opposed to an E minor which would be in A natural minor.
I hope this answered your question... I'm just woke up and probably aren't making a whole lot of sense :)
