You simply bend paperclips to form slots at the end and connect them to the ends of a battery. Then wrap wire around a round object to form multiple loops. Place the ends of whats coming off the loops into the paperclip slots, and place a magnet underneath. The loops will begin to spin.
You will need to use magnetic wire for this. I used some heavy copper wire to emphasize the construction, but the heavy wire doesn't spin. Also be warned that the wire will begin to heat up.
Simple enough. Nice Demonstration of a DC motor. Cool thing to have laying around.