The seller has the option of adding a note to an order and set the note for a buyer. For buyer note, the buyer will get an e-mail notification for every note added. And for the private note the only the seller will get the e-mail notification. This functionality can be located by selecting Orders tab on the left pane of the Dashboard, then scrolling to the specific order and clicking view button under the Action tab to open up the details of the Order and view the Note/Add Notes.

Dashboard→ Orders→ Items→ view(Under Action tab)