Kristina Sherk - Photoshop Layers Masterclass

https://www.sharkpixel.com/understanding-photoshop-layers

Use layers to add any element you can imagine to your image. One of the core pillars of Photoshop and retouching is layers. Incorporating layers into your retouching allows you to easily change parts of your image without degrading anything underneath it. In this course, I will clearly and concisely explain all you need to know about pixel-based layers, adjustment layers, layer modifiers, blend modes, blend if commands, and text and shape layers too.