Lay a large sheet of cardboard on your table.
Trace a simple image that you wish to turn into a stamp, onto tracing paper, then tape that image onto your blank piece of metal.
Place a dull pencil on the edge of the stamp design. Trace over the image, pressing hard enough to transfer the image onto the metal.
Trace along the design a second time. This will raise the metal further. Flip the metal over, and---using the dull end of a spoon---go over the inside of the image, being careful not to press on the lines that you just traced. This forces the metal image to pop out from the metal, and helps create the three-dimensional effect, when stamping.
Pull the embossing metal off the cardboard. Turn it over and affix the metal onto the blank stamp aperture via double-sided tape or glue. Dip the stamp in ink, and press it onto a piece of paper.