I understand nothing about why he left.

No, we know nothing of these people.

I told her nothing except that Ralu wasn't there.

The result of the investigation was, I'm sorry to say, disappointing. We found nothing.

I'm afraid there's nothing new in this post.

A: What do you want to eat tonight?
B: Whatever. (Or: Anything at all.) I don't care.
(And note that in the colloquial expression Oeru (ngaru, poru, etc.) ke'u, the stress in ke'u shifts to the second syllable: ke.'U.)

I work all day and all night, and you don't give a damn!

Pretty bad. He understands almost nothing and only knows eight words.

I don't hear anything in the forest. I guess some Skypeople were just here.

This (worthless) little hunter can't catch anything.

Nothing could be (seem/appear) more beautiful to me than a Pandoran forest that has covered in moss, except perhaps this world soon covering itself in peaceful well-being and the Na'vi language.