HBK and HHH?

OK Im a wrestling fan, but I'm still not clear on all the allances an such, Like DX, someone please explain them to me. Also Rated RKO. I know whos in each little "group" but how did they get started whats there purpose and such. And what about Cena whos he with? Try to make your answers not bais, Im not in the mood for haters.