Well, I think we explained that already. But as to rebirth itself, I'll explain a little bit there. According to the scriptures, there are about 32 different realms of existence. The human realm is one realm all by itself, it's a special realm. Animals and insects are another realm, and then there are about five or six that are basically hell realms and there are twenty five or something that are heaven realms. It's not really heaven and hell in the way Christianity makes it out to be as it's not totally black and white, there are grey areas. But in the biggest hell realm, it's as bad as anything Christianity teaches! The nicest heaven realm, it's lovely just like in Christianity, but according to Buddhism, it's impermanent. And this is important to consider, that every one of these realms is impermanent.
So as to rebirth, you get reborn according to your Kamma or your last thoughts at the moment of death. If you're not partly or fully enlightened, then you might be reborn up, you might be reborn down, there's no guarantee. For a person who is partly enlightened, there is a guarantee: evidently you will never be reborn down. If you're partly enlightened, you are guaranteed that within a short amount of lifetimes you will actually get fully enlightened. So that's fine if you are partly enlightened. Otherwise for the rest of us, there is always the possibility of going down. This is why we have to do a lot of good Kamma; we have to be able to think of all these good things, we have watch out for the thoughts at the moment of death.