A service is CLR type that exposes business functionality to Clients.In order to expose the Functionality as service,

1.The class/Interface  must be decorated by ServiceContractAttribute.

2.The Methods(functions inside class) exposed through Service must be decorated with OperationContractAttribute

[ServiceContract] //service contract
interface IHelloindigoService
{
[OperationContract] //method exposed via service with oepration contract annotaion
string HelloService();
}