x-y modulation has to do with the mapping of some property to a graph that you can mess with afterwards I think. In fl studio it should just kind of cloud everything over depending on where you put tha
X and the
Y. as for music theory, I would say memorize some scales, or at least what scales sound like. My process is usually to pick out bass notes I like then formulate chords on top of those bass lines. You can make every chord fit within your chosen scale, or you can... branch out. melody usually comes last for me, and I don't really put much effort into it. just pick notes in the same key as the bass + chords, it is almost TOO EASY. then again I am usually fine with entirely
blocky-ass melody styles, so maybe this is why such little time is spent on that.
anyways I don't follow that format all the time, and I would suggest that you get experimental with it too. I always like music made by people who know little theory.