I ship things to Australia all the time & have been doing it for about 10 years. Shipping to Australia is one of the most expensive countries to send things to. You will need to know the exact weight of the item and how you want to send it, air or ground. If you send it ground, it can take up to 3 months to get there. Some postal workers have told me 4-6 weeks, but I sent a Christmas gift one year at the end of October and it arrived the first week of February. I only send things airmail now. You will have to complete a customs form (there are 2 different types of forms & both are very easy to complete) they are provided free of charge at the post office. You will have to declare the entire contents of the package and indicate whether it is a gift (which is tax free to the receiver) or if it is goods that will require the receiver to pay additional custom taxes. It's really not any different than sending a package to someone within the U.S. it's just the customs forms that you need to complete. You should be able to find information on international rates on the US post office website.
www.usps.com. hth!