Once you've created your services, you must assign them to specific Locations and Users before you can schedule them on your calendar.
If services are not assigned to a location/user, they will not be available until this is done.
How-to
Assign Services
Whenever you add a new service, you must go into Settings ➡️ Locations and select the Services provided by the location.
You must also go into My Account or Settings ➡️ Users and select the services that you/other practitioners provide.
🎉 You're all set! Now, go to your settings page and make these changes so you can start booking appointments on your calendar.