First there's the character construction....
You end up with characters that may or may not look something like this...
Then you place the characters on a tiny animation background moving them a little at a time, shooting them frame-by-frame...
You're almost certain to end up with a great (and possible hilarious) animated flick. Of course since these are birthday parties you shouldn't forget the birthday part of the party at the end...
You can get more details and info on how to book by checking out this page at the NFB's site.