This mod works and I would like to make one but can't find any information to do so.

I... don't understand the question. Any skin with layers works for the mod.

Photoshop, Gimp, Paint, https://www.minecraftskins.com/skin-editor/ , https://minecraft.novaskin.me/ , https://www.minecraftskins.net/skineditor anything that can edit a picture. Worst case look up tutorials on youtube I guess.

And how would i make a skin that uses layers. Is there a program or site that i can use?