从国内买来的东西现在在墨尔本海关 我该怎样拿到东西？

You need to find a Customs Broker to arrange formal import Customs clearance for you, the reason Customs hold the Goods maybe Customs believe the goods value over AUD1000, you need to pay duty and GST

Once customs hold the goods, you must arrange broker to arrange clearance, you need to provide invoice and transaction to the broker. Cost is around aud 165 to do the clearance.