What are layers, how do they work, and how do you work with them?

What will be an ideal response?

Layers are like transparent overlays on which you can paint or place photos, artwork,
or text. Each element in a photo project occupies its own layer—the background is at
the bottom, and the other elements are overlaid in the order in which they are added
to the project. You work with layers in the Layers panel, where you can toggle their
visibility, drag to change their order, and add layer styles, effects, and masks. To make
changes to a layer mask rather than to the image on that layer, first select the black
and-white mask thumbnail to the right of the image thumbnail. The checkerboard grid
areas in the layer thumbnails represent the transparent parts of the layers through
which you can see the layers below.