I was happy to see that “How to Make a Zoetrope” was one of Google’s “how to” topics for the day. It’s a handy skill to have, to say the least.
Google links to the wikiHow tutorial, although there are countless others on the web (see below).
The resulting illusion has to be captured on camera from above (rather than through the slits). When viewed in person, the movements can only be seen through the slits, while looking through the top creates a blur.
Another informative tutorial can be found at the ever-helpful instructables site.
Makezine offers an complicated, electrical version for more adventurous dabblers.