How to command dedicated server

Hello everybody, I'l trying to work with Unet on a dedicated server, i can connect from client to the server but i want the client to call functions on server, i tried [command] but i'm not sure about how it work...

do [command] call a function in the server without having it in it's in own code? Or maybe it call the function written on himself (client) on the server?

I'm looking for a way to (if i'm the client) tell the server that i want to use his function named "test()", RPCs legacy was on the documentation the best way to do it but i'm not sure if it work with UNET ...

If someone know how to call function on server with being the client , tell me please.. If you know where i can find some complete guide / information / tutorial about how to work with dedicated server ...

Thanks for help guys.