You have to do 16 commerce units. This includes the 5 "core" (compulsory) units of accounting, microeconomics, stats, marketing and management. So you now have 11 units left to complete the commerce part of your degree. Now, leave that at the door for the moment.
To get a major, you need to do 8 units that are relevant to that field of study. Eg 8 economics subject. The units that count for a particular major usually have the same code - ECC is for economics, ACC is accounting etc. You should get a handout during enrollment that tells you the possible majors, and the units that you do to complete that major. You'll find that most majors have a few units that you must do to complete that particular major, but you will also have some choice as to what units make up a major. Take economics for example.
You have to do:
first year micro
first year macro
second year macro
second year micro
Then, you have to pick 2 units out of a selection of 4. This means you've done 6 units. You still have to do 2 more eco units for the major. For these there are about 15 that you can choose from.
Now, say you want to major in economics (who wouldn't
) you could do the 8 units outlines above. But, you'll find that first year micro is one of those 5 core subjects that you have to do. This can still count towards your economics major.
So, now you're sitting at 5 core units, plus 7 eco units to complete the major, so you still have 4 units to take to bring you up to the 16. These can be any subject from the bus/eco faculty (eg a marketing unit, finance etc.), as long as you meet some criteria, such as don't do more than 8 first year subject, and do at least 4 third year subjects.
You don't have a minor, only a major.
This'll all get explained to you if you go to enrollment, so if it all seems confusing at this stage don't fret.