Nipple clamps??

So what’s the deal with nipple clamps? How do they work & what’s the big draw?

I’ve always enjoyed my partner nibbling & sucking on my nipples and it’s a major turn on. My new partner also loves my nipples and brought up doing something more after our last rendezvous when he kept pinching them super hard to the point of actual pain.... I’m pretty new to bdsm so what do I need to know??