Power down the film projector. You do not want it on when loading the film strip as the lamp in the projector tends to make the metal sprockets and gears rather hot.
Attach the film reel to the front of the projector (there is an overhanging arm that holds onto the reel). Make sure the film rotates back toward the projector (the film needs to roll from the top of the film reel down towards the projector, instead of rolling from the bottom of the reel--similar to a roll of toilet paper).
Thread the film around the top gear. There are small sprockets that catch onto the holes along the side of the film strip. This allows you to tighten the film to the projector without the film becoming loose while it is playing.
Push the film through the opening by the projector light bulb, and pull it through the bottom of the projector. Once through, attach the film strip to the second, empty film reel. Make sure to attach it to the top of the film reel, then spin the reel several times away from the projector. This allows the reel to grab hold of the film (and prevents it from falling off while the film is playing).
Power on the film projector, then focus it towards the projection surface. There is a focus knob on the projector in case you need to correct any soft focus. Push "Play" and the film strip begins to play on the film projector.