Layer Masks are the key to successful composites. They let you hide parts of a layer, thereby revealing the details on the layer below. Often the best way to begin when cutting out part of a layer is with a selection tool, like Quick Selection or Magic Wand. You can then refine the selection before turning it into a Layer Mask. Layer Masks appear beside layers in the Layers panel. Highlight the little mask thumbnail and you can paint over the image with black to hide parts of the layer or white to reveal, giving you complete control over what’s visible or hidden.