Rpg Maker Developers Group

Hello.

I don't use the forums often so apologies if this is in the wrong place. I've recently decided to do parallax mapping instead of only using tilesets, and as such I've learned about overlay mapping. From what I've searched online, I've only been able to find Yami's scripts for overlay mapping (here). I've tried to follow the instructions as best as I can, but because the demo tutorial is no longer available on Yami's website, I am having trouble finding clear answers to my questions. They are, essentially, as follows:

1. What is the difference between a "parallax" and "ground" layer? Tutorials I've watched online usually call it ground and overlay, so it has me confused.

2. How do I find my Map ID? Yami's script requires that you label pictures with a prefix, map ID, and variable number. However, because I have not used many scripts before, I am unfamiliar with what the Map ID is, exactly. Therefore, I do not understand how to label the pictures.

3. What exactly are the variables? From what I can gather, it offers the ability to switch between different layers of the same type. Does this mean I can assign 3 different "light" pictures 3 variables (1, 2, 3) and then switch between them? How do I control which switch to what?

Apologies of this seems trivial or obvious. While I've had RMVXAce for a while, I've never delved into scripts much, so they still confuse me.