in what order are you meant to list the courses you want at the uac website. its hard because you have to rank in order of Atar rather than how much you want the course right?
No. You rank them based on your own preference.
Let's say you are interested in these courses (in this order): Macquarie Law, UNSW Law, UWS Law and USYD Law.
Then you put them in that order. Then now you get your ATAR which I will say, 99.8. This UAI will allow you to get into any course. But since you put Macquarie Law as your first preference, you get Macquarie and other preferences are ignored.
Now let's consider another situation. If you get 90.5 which won't let you into any course except UWS, you will get into UWS Law.