Photoshop is all about layers. I'll teach you how to do things Lightroom can't, like compositing two images together to replace a boring sky.
Layers are almost useless without layer masks. They control what part of a layer is visible, or what part of an image is adjusted. We'll create detailed masks quickly using selection tools.
Sometimes you need to adjust part of an image. Change a color. Brighten a face. Bring out a dark detail. We'll use adjustment layers with layer masks to define the area to adjust.
Your image looks great on your screen, but the print will not look as good! Smart Sharpen can compensate for the slight blur added by the printing process.