"Have to" 是一个情态动词短语，用于表示必须要做某事或者不得不接受某种情况，也可以表示义务、责任或建议意味。它通常在英语中用来表达强制性的、必须要遵守的规则、约定和法律等方面。
例如：
I have to go to work today.（我今天必须去工作。）
You have to follow the rules.（你必须遵守规定。）
They have to wear a mask in public places.（他们必须在公共场所戴口罩。）
We have to be at the airport by 6 pm.（我们必须在下午6点前到达机场。）
注意：在口语中，have to可以缩写成 "have got to" 或 "gotta"。
have to的用法如下：have to 后接动词原形。
Have to是情态动词 ,意思是“必须、 不得不”。have to的三单形式是 has to 。
I have to stay at home .
我不得不呆在家。
My mother has to get up early.
我妈妈不得不起床早。
have to /has to 的否定句分别在have to 或has to 前加don't 或doesn't.
一般疑问句在句首加do或does。
例如：
1. They have to go to Shanghai. 他们不得不去上海。
否：They don't have to go to Shanghai.
一般疑问句：Do they have to go to Shanghai？
Yes, they do.
No, they don't.
2. Tom has to study hard. Tom 不得不努力学习。
否：Tom doesn't have to study hard.
一般疑问句：Does Tom have to study hard？
Yes, he does.
No, he doesn't.