Creating a Service 
Before you can model a query or custom operation, you need to create a service, which functions as a bundling entity for service operations.
In the Service Explorer, select the Services node of your project.
Open the context menu and choose Create Service.
In the Create New Service dialog box, enter a Name (mandatory) and a Description (optional) for the service.
In the Service editor, select the Operations tab.
Click Add to add a service.
Depending on whether you want to model a query or custom operation, in the dialog box select:
Query
Custom operation
You have created a service.
A service should contain a set of operations such as a query or a custom operation. For more information about modeling queries and custom operations refer to Modeling a Query and Modeling a Custom Operation.