Hi Dan i will try my best to explain, it looks like the pic attached where the bait is not attached to the hook directly but a line that extends from the hook, called a 'hair', the bait is threaded through with a baiting needle, and secured with a bait stopper. i think u can hair rig any bait but most common is boilies and tigernuts. the idea behind the hair rig is, carp suck in the bait and blow it out, on its way out the exposed hook catches somewhere in the carps mouth and causes it to panick and run, thereby hooking itself.
Later
Amith