One of the things that makes Kingdoms of Camelot an engaging game is the ability to chat in "real time" with other players. The chat window is in the lower left corner of the game window. It has two tabs -- one for "global" chat and the other for alliance chat. The global chat is really just shared within the domain, not all players globally. When you're on the alliance tab, what you enter is visible to only the others in your alliance. (If they are on the global tab, they will see it, but with a note indicating that it was posted only to he alliance.)
more on how to whisper and the uses of whispering to come...
how to change default chat tab
Special Characters and Filtering
@a and @g