Learn about adjustment layers and layer masks in Photoshop

I've been using Photoshop for years, but I don't know what I'm doing. When I get stuck, I often turn to the YouTube channel Phlearn to learn how to do something. In this easy-to-understand 10-minute video, I learned how to use adjustment layers to make changes to all colors in an image and how to use layer masks to changes the colors of certain areas of an image. I wish I'd learned about these a long time ago.