You can keep track of your appointments by using the Service Status categories. The preset fields allow you to show when a session is scheduled and then to update the session to show it has been performed or cancelled. Once the session has been invoiced and paid, you can change the Service Status to completed. This helps you to keep track of who has completed their work with you, who still owes money and what action you may need to take.
You can add other categories if you need to. E.g. You may wish to add a “tentative booking” category to hold a space for someone for a period of time.