Wear gloves and glasses to make sure you don't get cut by a shard. Use the scissors to cut the top and the bottom off of the aluminum can.
Flatten the aluminum into a sheet.
Trace the shape that you want to cut out of the can using the pen. You can use a leaf or any other object to trace a shape out as needed.
Cut along the traced lines to carve out the shape from the aluminum.
Sand away any sharp edges and sand down the surface to give it a smooth texture.
Use the etching took to carve any patterns into the material that you want. You could outline them first with the pen but make sure the ink is removable first.
Decorate the piece using paint, glue, string and any other adornments that you want to use.