Quote: "Which one(s) is/are the easiest to understand?"
Variables and how to use them have been discussed
here. I even
linked the tutorial from Plystire, which is what I used to learn and know the variable system for FPSC inside-out. I also added the additional information from Flatlander, another developer that also knows and understands the variable system inside-out (he even made his own system that surpassed FPSC variable system).
There is no other way to explain it, and you either can grasp it or you can't.
There's no problem that can't be solved without applying a little scripting.