That's pretty much it. At the end of the holder, opposite where you insert the fim, is a a catch that holds the metal clip, which is attached to the film inside the sleeve.
You insert the pack, and you will hear/feel the clip operate, then you pull the sleeve until it stops. At that point the film is ready to be exposed.
After exposure you push the sleeve back down, then flip the lever to bring the rollers together, then pull out the the sleeve with the film in a continuous smooth motion. Flipping the lever releases the clip and allows all this to happen. You pull the sleeve out completely out of the holder this time, and wait the required time, and pull the sleeves apart to reveal the neg and print.
If you look at the holder you will see that the lever pushes down on a large metal tab. This is what releases the clip. If you want to process the film later you push that tab by itself and you can remove the exposed packet without processing. That way, you can process the film at home, and not carry the clearing bath around if you're in the field.
The last time I shot old type 55, the neg was stuck inside the sleeve and wouldn't allow the sleeve to be pulled up for the exposure. If everything works right the sleeve should be easy to pull up to make the exposure. If it isn't the pack may be no good.
Most people downrate the speed if you are looking for a negative rather than the print. The print will look very light in this case.
Pulling the sleeve out for processing involves a fair amount of force when the clip gets to the rollers. You may want to do this with the holder out of the camera, or hold the camera and the holder very firmly, if you don't.
Another method is to pull until you feel the resistance of the clip against the rollers, then flip the lever to release the rollers and finish pulling the sleeve. However, if you do it this way, it may not spread the chemicals completely to the end of the neg.