how do natives use you'd better?

is it true that it's impolite or even rude to use you'd better in a situation like a student talking to a teacher? how can i use it properly?

It might be rude for a student to say "you'd better" to a teacher. It all depends on the context, though. For example, "you'd better" sometimes indicates an order and of course ordering your teacher to do something is not appropriate. On the other hand, "you'd better" can also indicate a light suggestion. So, "You'd better give me a good grade." is definitely not good because it almost sounds like a threat, but "You'd better bring an umbrella tomorrow because it's going to rain." would probably be fine.