Create a regular comment

 Action    name: MakeComment
 

If you stand at the segment start and your cursor is on a segment name, IDA will ask you to enter a segment comment.

If this command is issued in the structures window, it allows you to change comment of a structure or structure member. If the cursor is on the structure name, it will be changed, otherwise the member name.

Otherwise this command allows you to enter a normal indented comment for the current item.

You can show/hide all comments in Comments Dialog.

See also

        "How to use the notepad"
         Edit|Comments submenu
         Repeatable comments
         How to use the notepad