how to apply visit to china

You should submit the former Chinese passport (the Consulate General will cancel its validity). If yours are not available, ID carrying Chinese name issued by Chinese authority e.g. birth certificate, driver license etc. are required (oth of the original and the copy). Other basic documents are your Australian passport, application form, photo, return ticket and hotel reservation. If you visit families/relatives, you need to provide invitation letter from China as well.
I don't know where you are living now, please refer to consular districts of Chinese embassy and consulate first, then decide where you should submit your application to.