Press 'G' on the keyboard or click Guild information icon to activate the Guild Information Window. Click on 'Command' to see the Guild related commands. While chatting in 'All' or 'General' mode, type in '/guild' command or '/g' command to chat only with the members of the Guild. Note that chat command for All chat is '/all' or '/a', general chat command is '/general' or '/e' and the command for Party chat is '/party' or '/p'.