Whether or not you want to peel the potato doesn't matter. Wash thoroughly and cut a slice lengthwise off the potato. Lay it flat on the cut side so it doesn't roll. Cut lengthwise into 1/4 inch or 1/2 inch slices, depending on the size cube you want. Stack a few slices on top of each other and cut lengthwise again the width you want. Turn potato so you can now cut across the lengthwise slices 1/4 inch or 1/2 inch wide. You will end up with cubes. If you are doing a lot of potatoes place the cut pieces in water while you are cutting the rest.