The frame code uses a grid system to determine the position of letters. The message is then written graphically as shown. The dot indicates the second letter in the frame.
The Romans invented the stick code. This was created by winding a leather strip around a stick of a special thickness. The message was then written on the leather and when unravelled would appear to be random letters. It could only be decoded if you has a similar sized stick.
A Code wheel is used to create secret messages by replacing one letter for another. The first letter in the message is the letter that matches with A on the outer circle so it can be encoded
MEET AT THE CLOCK
PHFFJ PJ JAF NTVNC