This ITIL core foundation video explains about the three types of services in the service strategy with a clear example.
Core service, enabling service and enhancing service
core service:
core service can be defined as a service that delivers the basic outcomes desired by one or more customers.
enabling service:
which can be defined as a service that is needed in order to deliver a core service.
enhancing service:
which is a service that is added to a core service to make it more attractive to the customer.