Congrats on your find. I've attached the instruction sheet, which will save you a lot of frustration, though by the time I managed to get the instructions, I had figured it out by trial and error.
A few key issues that are not obvious--
1. The film should have about 1/16" of play in the slot. Sacrifice a sheet of film or use a scrap neg to test it when you adjust the height of the reel. If you do it right, the reel will hold 12 sheets as intended. People who claim that the tank won't hold 12 sheets either have a bent reel or they haven't adjusted it right.
2. The film goes emulsion side in.
3. Curve the sheet in the direction of the reel when loading and it should slip right in, if you've adjusted the height properly.
4. If you are missing the metal band, you might use a rubber band to make sure the sheets don't slip out during development.
5. The tank holds 1200 ml. Fill time is a bit slow, so you might fill the tank and insert the reel and put on the cap in the dark, then proceed with the lights on.
6. If you're using one of the East European films with a soft emulsion, take care when removing the sheets to avoid scratches.