How Nukes work

I was watching a history channel show about the secret bunker made to save the government in the event of nuclear war and they talked about the history of nuclear weapons. One of the things they mentioned was the creation of the A-bomb and then the H-bomb. So I went looking for what was the difference. Never did find that out, unless one is a fission bomb and the other a fusion bomb.

But I did find out how they work on How Stuff Works