With 1.3 so close, you might want to hold off learning to make terrain for now. From what I hear the terraformer will work quite differently in the new version and be easier to work with.
I agree with anthon but for now you can also use the NL toolbox but i don't know where you can download it. Because it has a really nice terrain generator. I've been searching for a download link but i can't find it [:(]