What's "fuck off" mean? Is it different from just saying "fuck you?"

Native speaker’s answer
Rebecca
It means something very similar, and also has the added meaning of "go away." Thus, if you want to use very strong wording to tell someone to go away, you can say "fuck off." Ex: Who are you? I don't even know you, fuck off. Ex: Fuck off, dude. You just knocked me into someone else.