Once you start, you'll be told by your lecturers what books you'll need. You'll be able to buy everything on campus, from the Co-Op Bookshop (
http://www.coop-bookshop.com.au/bookshop ) or from the University Copy Centre (
http://www.usyd.edu.au/su/ucc/ )
The materials you need a basically divided into 2 parts - textbooks and readers. Depending on the subjects you do you may need both or only one or the other.
Textbooks are bought from the Co-Op. There are other places you can buy them from like
www.textsinthecity.com.au or
www.textbookexchange.com.au.
Readers can only be purchased from the University Copy Centre, and you can order them online to pick them up quicker. Rumour has is that this year, you won't have to buy readers anymore if you can't afford to, but you can get them in pdf format online from the library - one of the small things our SRC has done (apparently)
The other place to look for what you may need will be in MyUni once you have your login name and password under the MyStudy tab.
Don't fret too much. It'll become clearer once uni starts.