If you're going to allow your customers to choose from different services you offer when creating their bookings, you'll need to configure the service items first.
When adding services, they must already be added in Setup, lists as this is where it will pull the item from. If you have not already setup your services in Setup, lists, you should go do that now. Once added, return to the OLR setup.
To add these services to your OLR system, click the Online Reservations menu item and choose OLR Settings. Click Groom Services tab.
Your editing view:
Your customers view when making a reservation:
Once you have a list of services, you can use the up/down arrows to re-organize your list if you wish.