Click the calendar button on the menu on the left-hand navigation menu or by use the keyboard shortcut [CTRL+1].

The client assigned to this appointment. If set a email and text notification may be sent to the client depending on the Reason for visit settings. The dropdown is populated by your client list.
Determines the duration of the appointment, the default appointment location, and the content of the confirmation/reminders sent. If the duration does not match the selected start and end time it will ask you if you want to overwrite the reason for visit duration.
Defines which calendar the appointment will be assigned to. Defaults to the calendar that was clicked when creating the appointment.
Defaults to Reason for visit settings. In-Person, Telephone, or Video.
Timezone being used for the appointment. Defaults to organization timezone.
Defaults to date that was clicked when creating the appointment.
Defaults to the start time clicked when creating the appointment.
Defaults to the end time clicked when creating the appointment.

Save: Creates the appointment and closes the dialog.
Cancel: Discards all information and closes the dialog.