i went to unsw last year and this is how enrolment was there:
stood outside in a big ass long queue until they open the door and usher you in.
on the main floor there were all these signs saying stuff like "ARTS", "LAW", "ARTS/LAW", "SCIENCE", "ELEC ENG" etc with these enrolment people sitting under them, and you went and stood in another long queue
once you get to the head of the queue you speak with the enrolment person and choose your majors and any elective/extra courses you want and they dole out advice, all the time while people behind in the queue shift around impatiently and shoot off dirty looks at you.
after you finish talking, they mark down all these courses you are taking on a piece of paper (which i'm assuming is going to be the part 3 on the enrolment paper at ANU) and then you took the paper down and stood in ANOTHER big ass long queue, this time next to the UNSW toilets leading into their computer room where people looked at your courses and printed out a timetable for you
of course this is only for UNSW and ANU will probably do a few things differently, but if you're really uncertain over a particular point, ring up admissions and ask them. if i'm wrong, then come back and tell me so i can start stressing out too, but right now i'm pretty certain that you dont need to worry about anything right now except filling out the hecs payments declaration form