Please explain how this game works

I picked up Star Ocean First Departure today for about $5 (brand new, even!) The story part, I understand.

But...

I don't understand how the battle system works. I find myself just hitting X until all the enemies die. I don't think I am doing it right... There has to be more to it, right?

Also, the skill system doesn't make sense to me. Why would I want to learn how to whistle? I don't see the point..

Maybe I've just played too much Dragon Quest and Final Fantasy...

If you can give me an overview of how this game works (please avoid spoilers! pleeeease) I will love you forever.