UoC are just like HSC units. You just need to take 24 per semester.
And you pick a major, and on the handbook page there's just a long list of subjects. All you do for your degree is do every course on that list - or fulfill what it says about the list (so if it says 'pick 3 of the following', you do any three of what follows).
That's all it is. Once you do that, when you graduate, uni double checks you followed the rules of the list - and if you do, you get to graduate. If not, you're back to uni for another semester.
So for Commerce you have to do all the Compulsory core (eventually) and I think 4 of the Flexible core (eventually).
I say eventually because again, course order doesn't matter unless you consider prerequisites. So no doing accounting 1A until fourth year if you're going to be an accounting major, for instance.
