Hi Alex
I have uploaded some photos of the cassettes here
https://photos.app.goo.gl/UAhpp2TxCdnuwawG9
There are four parts to it. The main case, a lid for each end then a plastic reel that the film is attached to.
The length of film (Keep an old film to measure the length) is attached to the reel with tape and is is then put in the larger end open side up. You then need to roll the film up so it fits in the other end making sure you fit it through the felt seals at each end. Then put the caps back on and tape it up. Hope that makes sense. I have only practiced so far and have not loaded them with any unexposed film.
As the minolta cameras do not require perforations you can use all sorts of film. I have some microfilm to try at some point.
David