Remember, there are a few things that need to be setup before you can start adding appointments like adding your appointment types and adding clients.

There are a few ways to trigger adding an appointment:

1. Tap on the blue plus sign on the bottom right of the window and select New Appointment.
2. Use the keyboard shortcut ctrl-a.
3. Click anywhere on the calendar.

Unless you've specified not to, a notification will be sent to the client with the details of their appointment. More on notifications: How do notifications work?