Roll out your gingerbread cooke dough and cut out your cookies.
Take your knife and create a slit/wedge in the base of the cookie. If using a gingerbread cookie cutter, it's as if you're cutting the cookie in half but only going to the belly button of the cookie.
Bake your cookies following your package instructions. Typically it'll be 9-12 minutes at 350°.
Within a minute or two from pulling out the gingerbread cookies, recut your cookie with your table knife. Basically, follow the 'guide lines' that were created the first time you cut the cookie.
Allow the cookies to finish baking and cool on the tray.
To make your icing, combine your powdered sugar and water. You want it thick enough it won't run off the edge of the cookie, so if it's too thin add a bit more powdered sugar.