Deferring a program is only possible for commencing students. It is not an option if a student has already completed a term of study. Given that you have not yet commenced your degree, you are still classified as a commencing student, and can therefore defer your degree. This is possible for most of UNSW's programs, with the exception of co-op programs.
If you accept your offer via Accept Online, are enrolled in at least one course and then decide to defer, you can request a Deferment using
this link. To access this page, you are required to login with your UNSW credentials.
When your deferment request has been processed, you will be removed from any courses that you have enrolled in and you will be emailed a Deferment Confirmation letter, which contains information regarding the manner in which to take up your deferred place in a future term. It is important to note that you must apply to defer no later than the census date. You need to defer your offer by the deadline specified in Accept Online. UNSW states that requests after the particular date will be considered on a case-by-case basis and may result in your offer lapsing, which is a risk that you probably should not take.
When you start your degree and complete one or more terms of study, if you then wish to take a break from university, you can apply for program leave, also later than the relevant census date.
I hope this helps!