Once you connect to a service, you retrieve the operation or operations you want to perform, using ostc_Session::getOperation():
ostc_Operation * transfer = _session->getOperation("transfer");
"transfer" is the name of the operation you want to perform.
transfer is the operation, an instance of ostc_Operation.
You use ostc_Operation::setArgument() to set the arguments of the operation you want to perform. Once the arguments are set, you pass the instance of ostc_Operation to ostc_Session::doOperation() to execute the operation.
Click here for the example in context.