Just to clarify., the week of March 3-7 is known by the university as "Week Zero". During this week a number of programs are running. One of these is O-Week, which includes all the fun and excitement which is explained at http://www.oweek.unsw.edu.au
The other important thing to note is that during Week Zero some faculties may be running compulsory adademic activities. This may include things such as Lab introductions, etc. For full details check out https://my.unsw.edu.au/student/atoz/WeekZero.html
To find out whether you have any academic activities which you need to attend, check your timetables via http://www.my.unsw.edu.au.
The first of the 12 weeks in session one is week one, which is the week after week zero.