Woah woah slow down there
You get one offer and that's the highest preference that your eligible for. After you choose you should get an email from your uni with a little congratulations and what not from which it will direct you to a page to start your enrollment such as how your gonna pay your fees and setting up courses etc.
At Unsw were on a trimester system now so the usual is 3 subjects a term, in total 9 a year. Usually the finals are weighted heaps like all my finals have been at least 50% of the total mark. In Unsw CS so far has given me 2 assignments per course and for Maths you also usually get 1 assignment and 2 'midterm' tests and a final. The CS final is done on a computer where you live code to problems that they give you.
will direct you to CS at Unsw(if your planning to do it there) and you pick a 'major' and it should pop up a bunch of courses under the sections level1, level2 etc.. You usually do level 1 courses first then level 2 etc.. however you don't always have to follow this rule, like I'm doing a second year course this term in my first year.
Uni is stressful at least Unsw has been quite stressful for me. Your expected to pick up things really fast so be prepared! =)