Course
You'll need to refer to that for subject numbers / courses.
Firstly, it's not mandatory to choose a Key Program straight away, if you're still unsure, you can put it off till the Spring (2nd) Semester.
As noted:
The seven compulsory common core units are:
- 200336 Business Academic Skills (must be completed in first session of study)
- 200052 Introduction to Economics Methods OR 200032 Statistics for Business
- 200184 Introduction to Business Law
- 200571 Management Dynamics
- 200083 Marketing Principles
- 200101 Accounting Information for Managers
- 200525 Principles of Economics
So if you're not inclined to select a course now you can select, Business Academic Studies + another 3 (ideally) subjects.
You don't really need to worry about Majors and Submajors at this point in time. I'd be more focused on selecting the right Key Program, since electives are generally for 2nd year students.
And to answer your question about be able to cancel your Key Program if you started, you can. If you select the core units (as above) then you'll have no problem. If you do something within that Key Program, that will ideally be used as an elective for your new Key Program.
Also, if you've missed out on the Basic maths test, you can do it next Semester. No big deal really.
If you're looking to just register for your 4 core business units then you just go to MySR, "Enrollment" and go to "Unit Selection" and enter in the 6 key unit number.