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》

With all the lesson preparation I have to do I work 12 hours a day.

加上必须的备课在内，我每天工作12个小时。

《牛津词典》

I can't do anything halfheartedly. I have to do everything 100 percent.

我做任何事情都不能半心半意。我做每件事都必须百分之百地投入。

《柯林斯英汉双解大词典》

"But what will my duties be? Do I have to personally reject these three thousand good-for-nothings you speak of?

VOA: special.2010.04.24

The first thing I have to do is give you understanding of the physics of the gas discharge tube.

首先要做的就是让你们理解,气体放电管的物理学原理。

麻省理工公开课 - 固态化学导论课程节选

and I just want to be at home, not having to do whatever I have to do,

并且我只想呆在家，不用做那些我必须做的事情，

去溜冰场 - SpeakingMax英语口语达人

Now, there is legislation covering what I have to do if a concussion is suspected.

FORBES: When A Youth Coach Has Mike Shanahan/Robert Griffin III Moments

"I am not going to stop doing what I have to do, " she says.

CNN: BURNED BY HOME FIRES

It's something very bad, but if I have to do it, I'll do it.

NPR: Iraqi Refugees Struggle to Build a Life in the U.S.