Use the Magic Wand button to activate the Magic Wand selector. When activated, additional buttons will be visible that let you control the area selected and process the backscatter in that area. The Magic Wand starts in the Add to Selection mode.
While the Magic Wand is active, you can zoom in and out using the middle mouse wheel, and use the scroll bars to pan the image.
Select the Magic Wand button again to turn it off.