used to tell someone not to worry about something because it is not important

"I'm sorry I lost that wallet you gave me." "Never mind, I can easily buy you another one." “恐怕我把你给我的那个皮夹弄丢了。”“哦，没关系，我再给你买一个就是了。”

used as a way of emphasizing that, although a particular thing is true, the one you have just mentioned is more important or interesting

This is one of the best restaurants in the Northeast, never mind Boston. 这是东北部最好的饭店之一，更别说是在波士顿了。