Why Layer?

This is for Melissa, too, who asked why layers in Photoshop are good.

Layers are essential to Photoshop.  It is how the program works.  Basically what you're doing is creating different layers on top of your background image.  You can add a layer to add contrast.  You can add a layer to brighten.  You can add a layer to change it to black & white.  (And about a million other things.)  Layers can be adjusted and moved around to create different effects.  You can turn a layer off by clicking on the eyeball next to the layer.

It's like in traditional photography.  In dark room photographic processing you can manipulate your image in "layers" to get the desired effect.  There are filters and methods to make parts of an image darker (burning) or lighter (dodging), etc.  Photoshop is the same, except you can undo your layers if you want.

Did that answer your question, Melissa?