Please ELI5: I Don't Understand the Game's World

Hi, I'm currently in Act 3 and I'm an idiot. Because I don't understand how this game's world works. I don't know the difference between Lumina, Chroma, or Pictos. None of it makes any sense to me.

So Lumina is like...gun powder I guess? That you put on your body? Chroma is money but it also is used in attacks??? And Pictos seems to be weapons or whatever but it can also spawn Pianos??? And they're used as permanent buffs in the menus?! What are the light ropes and tethers? Are those lumina???

The Lumina converter makes even less sense and to be honest, I don't even know what it even looks like. is it Gustave's Arm??? But then there are....Lumina points???? Ugh, I'm just so confused.

I think the beginning of the game explained what each of these things are but it was kind of information overload for me. They told me everything at once and I just didn't mentally absorb it. Mechanically, I understand how they buff your character but as for how it all ties into the game's world, I just don't get it. Someone please explain.