you can use the "you have to" pattern to express something that somebody else really must do.

你可以用“you have to”句型表明一些其他人必须做的事。

have to 课堂 - SpeakingMax英语口语达人

You can say "Why don't you" when you want to suggest that somebody else do something.

当你想建议他人做某事时，你可以说“Why don't you~?”。

Why don't 课堂 - SpeakingMax英语口语达人