PROTECT AREAS WHEN PAINTING.
Sometimes when you paint you want to make sure that certain parts of the image won't be changes. When you paint your house, you use masking tape and drop cloths to shield areas you want to protect. You can achieve a similar result in Photoshop by selecting.
When an area is selected in Photoshop, none of the painting tools works outside the selected area. To protect an area from painting:
Photoshop ships with its tool palettes grouped in several floating windows -- for example, the layers, channels and paths palettes are together. You can customize these groupings to suit your own style of working.
To move a palette to its own window, grab it on its tab, drag it from its window and release it anywhere outside an existing palette window. To move it to another existing palette window, grab it on its tab and drag it to the center of that window.