Back to your original question; here is a link
There are links on that page that will take you into further explanation on Kamma, human birth, etc. Please note that Buddha refuted the idea of reincarnation, the rebirths we experience is more of continual existence of a stream of consciousness which is reborn into various realms of the (or lack of) senses. Don't spend to much time wrapping your head around what the difference is, it takes awhile to grasp the concept.
A quote from the link given that may benefit others:
"It is pointless to debate whether these realms are real or simply fanciful metaphors that describe the various mind-states we might experience in this lifetime. The real message of this cosmology is this: unless we take steps to break free of the iron grip of kamma, we are doomed to wander aimlessly from one state to another, with true peace and satisfaction forever out of reach."