小何，以你的汉语水平，去查汉语词典吧，不要再查英汉词典了。如果能查古汉语词典就更好了。

I saw your Chinese level is near native so I will write my answer in Chinese. 在表示“不要”和“阻止”这两种含义的时候，他们差不多，只是语气上的区别，“别”语气比较随意，而“不要”用得更广，书面语，正式语，口语都可以用，还有一个词叫禁止，禁止语气更强，更严厉一些，多用在告示上，比如禁止吸烟等）。 你的问题之前也有人回答过，你可以参考：https://www.italki.com/question/103069

most times, almost same, both means "don't". sometimes, it's different. For example, 1. 不要脸，you can't say 别脸 2. 不要命，you can't say 别命 these two examples above both want to express "don't want", not "don't" maybe there are other means, I can't remember all.

生活中用的时候都差不多，都能懂.....

我个人认为他们的意思很相近。有时候可以互换。interchangeable. 別， 指否定negative或者in spite of.....but... .不要，指don't. 别看她岁数大，可长得少相。despite her age she still looked quite young. 别动. don't move. 不要总是以为自己对。 don't think you are always right.