Yes, you are required to enter your appointment on the system calendar for online sessions. This way, your clients receive the email to join the session, and it shows up at the correct time when they log in to join.
NOTE: No PHI appears in the email to the client.
You will also receive a calendar invite when the appointment is scheduled. With any major email application, simply click ACCEPT or YES, and it should be added to the calendar associated with that email automatically. For instance, if you use Gmail, click YES on the invite, and that system appointment will show up on your Gmail calendar.