So you've got a cool juice box with a hole and some film. Who cares?
All that form is of no use without function, so let's get to that.
The light goes through the pinhole and exposes the film. So in order to keep the pinhole from constantly inundating the film with light, we need a shutter. The easiest way to do this is another piece of handy-dandy electrical tape. Slap a piece of the tape over the hole and pull it open to expose the film.
In order to advance the film, you'll need a car key or another type of key. Put the key in the EMPTY SPOOL'S reel and turn COUNTER-CLOCKWISE to properly advance the film.