To add a Service type begin in the PetExec menu under Scheduled Services-->Add Service Type. Service types added here will appear in the drop down box when you add/modify products & services. Service types that you add here will also be used in the scheduled services module when scheduling appointments.
If you select "Include in Scheduled Services Menu" you will see products and services for this service here, when scheduling appointments:
For more details on service types, see our Add Product / Services document.