As you already know, when viewing a page in the User Guide, you can view any notes you have previously created, as shown here.
As you can see, the user made a note about the discussion on Simulations. Also, notice that when the user opened the page upon which she had made her note, the Notes Frame displayed her previous note. Now, let's assume, that on reviewing the User guide, the user wanted to expand on her note.
To do that, she typed in her additional notes. When she started typing, a new "Save" button appeared below the Notes Frame as shown here:
After finishing her comments, she pressed the Save button, thereby saving her changes.