Carefully insert point of blade into tip of trimmer with blade edge facing right. Be sure to keep thumb and fingers away from the blade's edge. Then flex blade - pushing lower end to the left under the retaining hook. Soften area in hot water. Hold trimmer against callus or corn and pare down with thin shavings. Don't try to take off too much at once. The space between the blade and the razor guard is graduated. For heavy paring use the area closer to the blade point, while finer paring can be done using the area closer to the handle.