There are no light seals except for the labarinth door to the film spool chamber.
Open your bulk can saving the tape, the film is in a bag inside. Put the film over the screw with the payoff thru the door anti clockwise. Drop the round cover over and close the seal, hand tighten the lock screw, there is an arrow. The emulsion should be down, base up. Tape the film to the spool. put the spool in the can, put the can where you can crank the film stretching the film and making sure it catches the counter pawl. Install the door. Open the film chamber seal. There is a chrome lever so you can not open the seal if the door is not in place. Set the counter to 37 so you "waste" 3 frames. Then wind on as many exposures as you want up to 36 + 3 more. Close the seal, move the lever, open the door and cut the film near the counter pawl. Trim the leader.
Repeat for each roll.
I had one of these since 1960 and always had an issue with the film disengaging the counter and the film can rotating popping the door open. I inherited a later model, grey plastic, and examined the new design. They added a tab in the door near the film can lip to stop the rotation and added a bit of plastic near the pawl to hold the film down. I modified the old black 66B with the same upgrades and never had a problem again.
i suggest you load in a dark room while cranking incase you have the same problem with the door popping open. That was my original solution. The add on pieces are a much better solution.
Clean all the felt lips so you do not scratch film. Keep film cans in a sealed plastic bag to keep them clean. This is the one big killer. I have never scratched film, but many have.
Send me a pm and I can send you a photo of the cover mods. They are just pieces of plastic from the hobby shop and installed with weldbond glue. Never use the tube stuff they sell to kids for airplane kits. It is sniff proof for safety. Downside is it is very weak.
The second problem is the tail is exposed fully and you can still take pics on it, so watch the film counter.