These are fun cameras!!
Yes the button on the right top of the camera lifts to accept the new roll of film.
The button on the left top lifts to accept the take up spool.
I use the J&C 620 film and after you have taken the tape off the roll of film and thread it into the take up spool and turn the left top knob to get the film started, then close the back.
You then continue to wind the left top knob until you see a one in the red window on the film back. The very first time I loaded mine, I went past the 1st frame because I wasn't quite sure what I was looking for. There are markings so you'll be fine.
I only open the little door covering the red window when I am advancing the film.
So far, I have had no fogging.
You do not need to return the film to the original spool.
Since 620 spools are hard to find, you should try to keep them. If you use a lab, tell them to return the spool to you after processing.
You can find the manual at the Yahoo group called: OlderKodakManuals
You will have to subscribe to it and then look in the files section. It is a zip file full of .jpg pictures which are the scans of each page.
I now roll 120 film onto my 620 spools. Do this in the dark though. I also save the nice little film containers that J&C ships the 620 in. They are nice to keep exposed film in.
Hope this helps.
Cody