Where should I send my application form and relevant documents?

Your visa application should be handed into Embassy of China in Canberra. The Embassy accepts mail-in visa applications from South Australia but they are not responsible for any loss, damage or delay of your passports/documents during mail-delivery. So, you'd better go in person, or by someone entrusted. For detailed mail application procedure, you can refer to official website of Chinese embassy.
Original passport is required. Fee for a single entry visa is A$60 and mail handling fee is $10.00 per package.