You won't have to write 50 page reports, but for some qualitative content intense subjects like Management you will need to write essays in the vicinity of 2,000 words. You will mostly analyse statistics in the subject of Statistics, but given its importance you'll come across it in pretty much every stream of Commerce.
It's really difficult to provide with pinpoint accuracy a description of what Commerce is like. Generally you'll probably find it interesting in that you will be able to tell it is directly useful knowledge, relateable to the function of businesses, e.g. it is easy to see how Accounting fits into a Business's overall operation, but also boring in that much of the subjects are textbook-reliant and you don't get to think critically or "outside of the box" as much (this is something you'd do more in Management or Marketing).
Generally though, it is a degree where the more time and effort you put into studying your textbooks, the better your results will be. The majority of your homework/exams are practise questions and problem questions, as usually in exams you will be given a hypothetical scenario and apply your knowledge of the material learnt to that hypothetical (so this is very much like how high school Math functions I would say, having not done Business Studies or Economics in high school).
By your second semester you'll be able to see pretty clearly that Commerce is very much a "same shit, different calculations" degree.
tl;dr: What you will do exactly in it is learn the relevant calculations and what they do for each respective subject, practise them through your homework and tutorial work, and be examined on them through hypothetical business scenarios (usually). It's virtually only in Management (and generally qualitative content based subjects) that you will be required to write essays/reports, and they will likely never be near 50 pages length.