Layering allows you to manipulate selected portions of a graphic or photo. You'd select the sky out, for example, to change it without affecting the rest of the picture.
For example, the Biden graphic I made below. I wanted to use Clinton's hand gesture and could not find a decent photo of it. I got the hands and took them off Bill. For Biden, the color, size and texture had to be changed. It's not perfect because I was in a hurry, yet most people wouldn't notice the details.
I just painted the lipstick on.
