How do I create a SysOperation service in D365FO?

A basic SysOperation process normally has three pieces:

1. Contract — parameters.
2. Service — business logic.
3. Controller — launches the operation.

Example service:

class MyOperationService
{
    public void process(MyOperationContract _contract)
    {
        str value = _contract.parmValue();

        // Do the work here.
    }
}

Keep the actual business logic in the service or a separate domain/service class. The controller should not become a 500-line business logic class.