On the server, to send a message all you have to do is /msg <player> <message>, if a player sends you a message and you want to respond to it without typing the whole thing out, just do /r <message> and it will automatically send it to the player. If your talking about the forums, you click on someones name by their post or go to their profile and click on "Start a Conversation".
Formerly known as HavocMC, Havoc Games has been pushing the limits of vanilla minecraft since 2012.
Home of The Mining Dead, Mine Wars, and Craft Theft Auto.