To pull out a film, first pull white tab out at medium speed in a straight line. This will bring out the picture pack's black tab in a separate slot. Pull the black tab out and start timing for development--depends on film type and temperature of your location. Then when time is up, peel print (it is gray-backed) off the negative.
Your pack is empty if you have used up either 8 or 10 films, depending on film type. I could say it might be empty if no more tabs come out--assuming nothing jammed inside the film holder!!!
To reload, take your thumbnail and slip under the metal bail (clip) on the right side of the holder (on the tab pulling side). Pop the bail out and swing it and the film door open. Pull out the empty film pack. Check the rollers for leftover goop from film developer pod. Lift out the rollers on their red plastic clip and clean with damp cloth. Resist temptation to scratch off hardened goop deposits with fingernails! That can scratch the rollers--I think Polaroid info said that. Insert rollers and click back into place.
Open your new film and remove from foil package. Lay the NPC back open on a table in front of you with hinged end on the left. Hold the film pack with the tabs on the right and black paper label covering the film window facing away from you. Place the tabless end of the film pack into the holder first and push left and downward to snap it in place. Make sure the tabs are fluffed out to the right side and not squished beneath the pack. Close lid leaving black tab sticking out. Latch the bail. Make sure the darkslide is inserted. Pull out the black paper cover tab. You're ready!
Please-- others chime in if I led this shooter astray!