A Service in checkAppointments is the reason for the appointment, the crux of why your client is booking with you. There is a lot of functionality here, including the ability to:
There's documentation on each of these additional items found in the related links, but on this page I am just going to show you how to add a new service offering.
To start navigate to Setup->Services
Then click on "Add New Service" on the top left (we talk about Personal Reasons and Editing services in separate documents)
There are three tabs that you will click through to define the information around the service you're adding which include "Service", "Location Hours", and "Staff". We go more deeply into what each of those mean in separate pieces of documentation, but suffice it to say that the:
Once you have finished going through all the tabs, there is a "Save" button at the bottom of the "Staff" tab. Make sure to hit that to commit your service!