Your student card will be issued on your first day at the college. It is an official document and can be used as a proof of identification at the bank for example.
It entitles you to discounts in transport as an international student. You can only get this discount if you apply for it online (see this website) for further details ask at reception.
You will also get a 10% discount at Subway (only valid for the Subway located in the same building as Strathfield College) on presentation of your card.