There is a global settings page where you can control your "Booking Schedule" which applies to all of your appointments and services.
In addition, each and every service you offer has its own custom schedule that can be activated by clicking on the following icon:
Click on the calendar icon at the top of the service settings
Select Custom Range and select dates and then the days and hours within that range.
This will come in handy if you have a specific service that you would like to offer outside of your general booking schedule.
Hope that helps!