Use the light side of the file, in long and light movements, from the edge towards the center, to give your nails the desired shape. To preserve the strength of the nail, do not file the external sides of the free edge too much (the most fragile part). To finish the job well, eliminate any roughness by making small vertical movements, from bottom to top and from top to bottom, with the tip of the file. This also helps to "weld" the 3 layers of the nail together.