The Magnifying Bar is set along the right side of several of the tools. Sliding the bar downward, increases the size of the image. Sliding the bar upward decreases the size of the image. The bar can set the magnification from between 1/10 and 10 times. (It is 20 times for the Edit Tool.)
Clicking the "Zero" button at the bottom of the bar, resets the magnification to one, which makes the image appear at its natural size.
Magnifying the image is useful for picking out fine details and doing fine positioning while your are editing the image. Magnify the image does not actually resize the image. It only temporarily magnifies it. When the images is saved, it will still be its natural size.