David H. Bebbington said:
What George has described is the single-sheet 545 or 545i holder. What you have is the pack holder. With this, if you pick up the holder so that that its back is facing you (i.e. side with the sheath is away from you), you should have a latch with the word "Polaroid" on it facing you. At either side, this has milled finger grips. Using these, pull the latch off the end of the holder back and allow it to swivel out of the way. The holder will now hinge open. Inside are pictures showing how to remove and clean the roller assembly (unlike the 545i back, the 405 gets very messy in use and will need cleaning every time it is reloaded). You can clean the rollers under a hot-water faucet with a toothbrush, drying them thoroughly before replacement. You can then insert the film pack so that the protruding tab points out of the end of the holder towards the handle. Close the back, re-engage the latch and pull the tab firmly but not too hard or abruptly. The tab for the first Polaroid print should then emerge from the slot in the end of the holder, which is then ready to use.
PS: The 405 holder will of course only fit a Graflok or international back which has a removable focusing screen assembly. Does your camera have this?