Sending Messages to other clients

I'm trying to make a two player game where one player is the server. I want both players to send messages to each other but I'm really have trouble getting two-way communication going. just a few questions -

does the server player have to send his message to the other player via NetworkServer.SendToAll?

does the client player have to send his message to the server player via m_client.Send?

if i wanted to add more players, is it possible to do sort of a peer-to-peer setup, where any...

Sending Messages to other clients