To add a New Appointment click on the Plus button in the top right bar

Alternatively, you can add a New Appointment via the Plus button on the Calendar Page.
When you add an appointment it can be an appointment for
a service
a class
a package
a private appointment

To find how to add each one, see below:
How to add a Service appointment click here.
How to add a Class Session appointment click here.
How to add a Package appointment click here.
How to add a Private / Blocked Time appointment click here.