You have a camera that takes 620 film - the exact same format of film as is on 120 spools, but on a smaller spool. 620 film is no longer manufactured, and for some reason, you want to used the camera. (Cameras that use 620 film tend to be really cheap. Really really cheap.) So you need to get film on your 620 reels.
Some web sites, ususally those that sell film pre-loaded on 620 spools, will lead you to believe that this is rather difficult. It is not, and with a little practice, it can be done successfully every time.
First, obtain a few 620 spools. You generally have one or two with the camera, and more are usually available at older camera stores, cheap - expect them to be in the $0.25 - $1 range. They (like everything else) are also readily available on eBay. Get a couple rolls of 120 film, including one that you are willing to sacrifice.
Take the roll of film to be sacrificed, and, in daylight, roll it tightly (but without pulling it) onto another 120 spool, as would happen if the film was normally run through a camera. Then take the very end of the paper, put it in the takeup slot of the 620 spool, and begin to roll it onto the spool, slowly. As soon as you get to the film, be sure that it, too, is rolled on, perfectly evenly.
Continue rolling the film until you get to the point where the film attaches to the paper - there should be no wrinkle here - it should be even. If not, start over until you get it right. If it is even, roll till you get to the beginning of the roll. Repeat a few times until you get the hang of it.
Now start working with a good roll of film. In a perfectly dark room - no safelights - this is photographic film - do the procedure as described above. A changing bag can also be used to the same effect. I generally use a rubber band to hold the paper down, though tape may also be used.
Note that the use of high speed films, such as Ilford Delta 3200, are not reccomended in cameras that take 620 film, as such cameras tend to not be completely light-tight. Also, if you are using a commercial photofinisher, be sure to tell them that you need your spools back.