that you or others or both of you take a particular course of action.

可以建议你自己、其他人或者所有人采取一种特定的行为。

Why don't 课堂 - SpeakingMax英语口语达人

Or you can say "Why don't we~?" when you are suggesting that you, as well as others, take a particular action.

当你想建议自己与其他人一起做出某种行动时，你可以说“Why don't we~?”。

Why don't 课堂 - SpeakingMax英语口语达人