7. Layer Masking
When working in Photoshop, you'll often need to combine multiple images together into a new composite image. Those original images, however, may have backgrounds or objects that you no longer want. This is where Layer Masks come in. Far superior to erasing pixels, Layer Masks allow you to hide (or mask) part of a layer using powerful painting and selection tools. The more you work on combining multiple images, the more you'll find yourself using masks.
The mask is the black-and-white area attached to the layer thumbnail. It contains all of the transparency information that the layer needs to isolate the flower from the background.