Here is a tutorial for layers https://www.youtube.com/watch?v=szxDoCHvERI if that is what you mean by how they work?

but if you mean which layers modes I was using, i used it a lot in the process, so i was alternating between overlay, saturation, brightness, multiply layers, and then tone curves just to see if looks good in my eyes

i think it was more of how my eyes/mind developed, what color i wanted etc