They attach to the end of the tag line that is attached to the trolling pole. The wire off the the gurdy goes through it on down to the cannon ball. The wire has a brass or plastic small ring, called a “stopper’ attached to that jams in there, then the line swings away from the boat and hangs off the pole.
By attaching the stopper at different places on the wire you can set the dept of your trolling line which your lures etc are snapped onto.
Sorry for lengthy explanation.....
Cheers