For all its tremendous complexity and variety of features, perhaps no aspect of Photoshop is more important than layers. If you are new to the program, this excellent video tutorial will show you everything you need to know about layers, including what they are, why they are so useful, and how to employ them in your work.
Coming to you from The School of Photography, this great video tutorial will show you everything you need to know about working with layers in Photoshop. Layers are so fundamental because they allow you to separate different components of an image, whether those are adjustments like contrast or sharpening or sub-images that help to build the overall photo. By separating these pieces, you can work on them non-destructively, meaning you can easily adjust them later on or even take them out of the photo without changing the foundation image you started with. When you combine them with layer masks, you can apply precise adjustments wherever in the image you like. It is generally a good idea to start using layers as soon as possible, as they will give your editing capabilities a big boost. Check out the video above for the full rundown.