Hi Lou,
The ball swivels thread into the hitch arms. The hitch pins (part E: also called secondary safety pins) pass through the eyelets into the receptacle ends (part D) that have been threaded onto the skewer (part C). That skewer should be going through your axle in place of your regular skewer. If your bike does not have quick release hubs (uses skewers), the trailer cannot be mounted to you bike.
Thanks,
Tech Support