Why can't i chat in minecraft?

So when i type something in and press enter, all it says is "Unknown Command, /help for help".

I went to chat settings and it's all correct, but I can't say anything on servers.

Sounded like you're pushing / to open chat. That's only for commands like switch game modes. Just push T, but you can change it by pushing escape>option >controls

Hope I helped! Let me know if this doesn't work and I'll try to help some more