Let me know [=tell me] if you're going to the party.你要是准备参加聚会，请告诉我一下。

Please let me know if there's anything I can do to help. [=I would like to help; please tell me if you need help]如果我能帮上什么忙的话，请告诉我。

He's not sure what time he'll arrive—he is going to let us know.他不确定他几点到到时他会告诉我们。

She let the staff know her decision. [=she told the staff her decision]她把自己的决定告知了全体员工。