Welcome to AN!
I'd really like to know if the Admission Information each universities which show the lowest, median and highest ATAR result from the students studying, can determine your guarantee of entry for a certain course?
Kind of. It's a bit more of a guideline, if you will. Some courses have been more or less consistent for several years, whereas others might jump around a fair bit, depending on the year.
The most important part is not so much whether you pass the previous year's lowest ATAR, but whether they have an available spot and whether you will be high enough on your desired institute's list to get said spot. For most courses, this is purely based off raw ATAR + any adjustments due to SEAS (i.e. special consideration) and/or middle band subjects (also known as subject bonuses), where available, as well as fulfilling the prerequisite subjects (rarely they'll let you get in directly from high school without some sort of bridging course). On the flip side, there are degrees (e.g. design, med, fine arts) that require you to undergo interviews, other tests and/or other activities/ assessments to consideration for said spot in whatever course you're hoping for.
Any tertiary institute can only feasibly take a certain number of students before things go downhill fast, so that's how the spots are limited. If it's a highly desired course, then your chances start to become a little slimmer. So it depends on course, demand and competition, in a sense. Does that make sense?
Say, if you achieve at least the lowest ATAR score (or maybe a bit higher) accepted in that year, do I maybe have a chance to study that course?
Short answer, generally yes. Usually it's heightened if you at least achieve the previous year's lowest ATAR, however, it really depends on demand. See previous answer. However, the fortunate thing is, if you're Victorian (I think NSW does a similar thing), VTAC (the guys who'll be the middle man during the transition between high school and uni) have a preference system. Therefore, even if you don't quite reach the lowest ATAR (although you'll still most likely need to get the prereqs required), you can still place your desired course as Preference #1 for a chance at said course. Nonetheless, you should ultimately be trying your hardest to achieve as well as you can and not rely on this to get into your desired course.
Or is there other factors that contribute and that the students have done to actually be able to get into that course? >_< Or is it just achieving the study score prerequisites of subjects and you'll be fine?
See above. SEAS, subject bonuses, prerequisite subjects (and their raw SSs) and maybe some other criteria (e.g. interviews, portfolios, performances) may be required, depending on the course.
I don't really know, but I'm expecting the least so it would be great to know if I stand a chance to have an opportunity to actually get into that course or not...
Which course are you referring to here? We can be a little more helpful if we know what direction you're hoping to head towards.