Tony1969:
There's an Advisory Circular on the subject (check the FAA website for AC 27-2, which I believe is the latest version).
But none of it is in layman's terms - believe me. I'm an experienced engineering test pilot, and it took me over a year working as a certification test pilot at Transport Canada to begin to understand the subtle and very complex nature of the certification requirements. Even then, there were things I didn't understand until much later.
I'm curious to know why you want to know the certification requirements. Not a cheap, quick or easy process.