UNET | How to use network messages?

Hello, I am looking for information about Network Message and how to use it. What i wanna do is to communicate each player with the server, for example the when the server have "n" numers of connected clients, it choose a color for each client. I think the server must changue a varible in each client to give him a color. I read this:https://docs.unity3d.com/Manual/UNetMessages.html but i think it is not totally complete. What i know is using network message is like to use Rpc or Command, but I dont understand it. Can anyone explain me Network Message and how to use it? or give me a completely tutorial about it? What i know about using network message: is similar to use Rpc and Command.