You are welcome to enrol in any class that you meet the prerequisites for. Use your advisement report to ensure that you do not take courses that cannot be used towards your degree requirements by accident. You are welcome to do so on purpose if you choose to.
To see how prerequisites are organized go to: the Academic Calendar > Most recent year > Course Listings > Search (Filter) by Subject (Prefix) > click on a class to see the prerequisites, then click on the prerequisite classes to see what they require. This will help you to decide which classes are most important to take this year
Prerequisites can be specific classes, levels, a faculty, or a program within a faculty, specific grades in a class, or your cumulative GPA
Antirequisites are specific classes, levels, a faculty, or a program within a faculty that will prevent you from taking a class.
Co-requisites are a class that you need to at least be enrolled in at the same time, if you don’t already have a final passing grade.