As we've discussed, it is critical in Photoshop to work non-destructively, and I will consider layers in Photoshop the hub or center of a non-destructive work-flow.
Layers are essentially pieces of our image that we can stack on top of each other. If those pieces of our image are separated onto different layers, we have much more control and flexibility when using those layers. This is much better demonstrated than described. So let's take a look.