To add a character, simply type it; it will be added to the left of the current position. This also includes the newline character; to start a new line, press carriage return.
To instantiate a def, use .
will prompt for the name of the def in the command window with I>; type the name of the def and press RETURN .
will insert an instance of the def to the left of the current position and move the tree cursor to the first parameter.