Erasing

The Eraser and Magic Eraser tools let you erase areas of an image to transparency or to the background color. The Background Eraser tool (Photoshop) lets you erase to transparency on a layer. You can also use the Auto Erase option with the Pencil tool to erase the foreground color to the background color as you paint.

If you want to erase the background of an object with intricate or wispy edges, use the Extract command. (See Using the Extract filter (Photoshop).)