You can add to or subtract from an existing selection to fine-tune selection borders. For example, you could make a donut-shaped selection by first making a circular selection and then subtracting a circular selection within it.
Hold down Shift (a plus sign appears next to the pointer) to add to the selection, or hold down Option to subtract (a minus sign appears next to the pointer) from a selection. Then select the area to add or subtract and make another selection.
Click Add To Selection or
Subtract From Selection
in
the options bar, and make another selection. (The Add To Selection
and Subtract From Selection options appear in the options bar when
any selection tool is selected.)