Please, I don't understand what I have to do.

我的确不明白我该做什么。

《牛津词典》

I doubt I do not understand.

我想我没懂。

youdao

I am a savage and I do not understand how the smoking iron horse can be more important than the buffalo that we kill only to stay alive.

我是一个野人，我理解不了那冒烟的铁马怎么会比我们用来维持生存才宰杀的水牛更重要。

youdao

I do whisper the description to him sometimes, though you can see people around don't understand and they're watching us like 'What the ...?'" "'Tell that woman to shut up!'

VOA: special.2010.03.01

I didn't expect it to do this. If you understand why it did what it did, you're half way there.

这样运行的啊，如果你能弄明白为什么,它这么运行，你已经完成了差不多一半了。

麻省理工公开课 - 计算机科学及编程导论课程节选

But I do also understand the need for advertisements.

但是我也理解做广告的需要。

广告泛滥 - SpeakingMax英语口语达人

So I understand how -- I do this every day -- I understand how someone can do a static analysis, order of battle, numbers of weapons and things like that.

WHITEHOUSE: The White House

How do I explain to my children what I do not understand myself?

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The only thing I do want to make sure you understand is when I do visit Alaska, it's going to be during the summer. (Laughter.) So I just wanted to be clear about that.

WHITEHOUSE: President Obama Opens Tribal Nations Conference