If you want to write something between two input-output pairs, put you cursor at the end of input line that is above where you want the comment. Got to the "Sessions Command" icon and click "Split Session". A new line will be inserted  under the output for you to type in.  The "Sessions Commands" icon is the third of three identical icons in the lower part of the tool bar. It is just to the left of the GO icon.  See attached.