In addition to the above codes there are procedural conventions for use by the sender and receiver of messages.
Used by Sender
AAAA = Attention; I have message are you ready?
EEEEEEEE= Error; Mistake made, I will begin with the last word sent correctly.
Pause= Period; End of word.
AR= End of Message; Did you get it?
Used by Receiver
K= Go Ahead; Start sending.
IMI= Repeat signal; Send again, I missed it.
T= Word received; to be used upon receipt of each word.
R= Message received; ok.
All of the signals using multiple letters are sent as if one letter. That is there is no pause between letters during transmission of these procedural signals. So the code for "Attention" which is 4 A's, would be dot dash dot dash dot dash dot dash, then a pause.
This can take time to learn, but may one day prove invaluable. Practice with a friend and get good, you'll have a blast!