What is a WCF OperationContract? I dont really understand what it does
Answer
WCF uses an opt-in model to define what belongs to one of its contracts. In a service contract interface, only methods decorated with [OperationContract] are exposed to the client. That means that, in the interface below, if used within a WCF service, a client could call both Add and Subtract operations, but not Multiply.
[ServiceContract]
public interface ICalculator
{
[OperationContract]
int Add(int x, int y);
[OperationContract]
int Subtract(int x, int y);
// Not decorated
int Multiply(int x, int y);
}