你不用走。 You don't have to go. 你不要走。 Don't go. 你别走。 Don't go. 今天是星期天，我不要上课。 Today is Sunday,I don't want classes. 今天是星期天，我不用上课。 Today is Sunday,I don't have classes. *今天是星期天，我别上课。 别 can't be used by first person 不用 means there is no need to do something. 不要 means the subject wants to do something,but the speaker don't want,or ask him/her not to.

1. In imperative sentences, 不要 and 别 maybe can both be translate into "Don't" in English, for examples, a. Don't be late !—— I think you can say "不要迟到！" or "别迟到！" interchangeably b. Don't swim here !——“不要在这里游泳” or “别在这里游泳” interchangeably 2. 不用 can also be replaced with "不需要" or "用不着", which in English can be translated into "needn't (do)", for examples, a. I needn't go to school tomorrow.——我明天不用上学 or 我明天用不着去上学 or 我明天不需要去上学。 b. You needn't tell me this secrect.——你不用告诉我这个秘密 or 你用不着告诉我这个秘密 or 你不需要告诉我这个秘密。 3. In un-imperative sentences, 不要 may be better to translate into "don't want " or "woudn't like " or , which stands for the person's willing to not do something, for examples, a. I (don't want to/wouldn't like to) go to Ireland by ship——我不要坐船去爱尔兰 or 我不想/不愿意坐船去爱尔兰 b. Sherry (doesn't want/wouldn't like) this pirated book——Sherry不要这本盗版书 or Sherry不想要这本盗版书 4. 别 seems to be used in imperative sentences generally and I can't think up the other examples at once.

不用 是个很委婉的词 你可以说 不用谢 不用你帮忙 可是 别人还是会说谢谢 会帮你忙 而不要是 do not fuck me 别是 dont fuck me

不要and 不用 means a reject or "do not" in more strongly way if you use "別" to express reject or "do not", it seems like a suggestion but, of course, you can use "別" in a strong intonation, it will sound like an order or a command

学习汉语，重点难点就在不要简单地把英语和汉语划等号，也不要不汉语的一个词与另一个词简单地划等号，认为两个词是同义词就可以同样使用，汉语的灵活性就在于一个词与另一个词的搭配关系上：几个词在一个固定的语境中，可以是同义词，但是加上搭配的词以后，意思就完全变了。汉语的另一个特点就是约定俗成，一个词的用法在某一时期某一地域可能被认为是错的，但是用的人多了，大家都认可了，也成对的了。