It isn't tough.
You need a dark bag or dark room.
The bulk film.
Reloadable Cassettes with spools. Normally sold together.
Masking tape.
Scissors.
Marker.
The dark bag is for taking the bulk film out of the shipping/storage box and putting it in the loader and getting the tail threaded. Once in the loader, you are done with the dark room/bag.
Keep an example roll handy.
The tail is threaded through a light trap into a small chamber where, in the light, you use the masking tape to attach the spool and then put the cassette in place around the spool. (Some loaders require the light trap to be manually opened or shut.)
Next the cassette is stuffed into the chamber much like sticking it into a camera, a door is closed, and a manual winder is inserted.
Set the counter, I start at -3.
Crank the winder to 12, 20, 24, or 36.
Pull the winder, open the door, push out a bit more film tail, enough to attach another spool and enough for the leader on the roll. Cut.
Shape the leader per your sample. Next.