Question

I'm new to the graphics making and I looked through the tutorials but I can't find this anywhere. It's pretty basic since every icon tutorial has it but its a big thing. I use Adobe Photoshop and I was wondering does anyone know how to make layers? Like when you have a pic. how do you put another layer on it? I see tons of tutorials that go "Then make another layer and set it to opacity 80% lighten. I know about the optacity stuff but I dunno how to do the layers. If you don't have Adobe could you still do the steps of how u add layers? Maybe I can try to follow it.

Thanks!