1. He traded the fly on the string to comfort a woman's baby so the mother gave him some mandarins 2. Gave the mandarins to a thirsty silk salesman who gave him the rolls of silks in return. 3. The silk rolls to a man with a tired horse (later helped to quench the horse's thirst by a river) 4. Finally gave the horse to a samurai (whom he and his men rolled out to battle) for his mansion
Which was how that story went, as he told his new-found friends in the end! Quite the charming book, if I do say so myself!