Courses are divided into compulsory courses and elective courses, and compulsory courses are compulsory courses. The significance of elective courses is that you can choose the time of class in the same year, which can be one year earlier or one year later (but it is recommended to follow the normal class system because some courses are coherent and affect your understanding of other courses), or you can choose your favorite teacher.
Let's just say that the compulsory course is to choose a teacher, and you can choose a time when you have time (for example, you like to sleep late and choose an afternoon class). However, it should be noted that there is a limit on the number of students in each course, which does not mean that you can choose if you want to. Elective courses are really free to choose, just learn what you are interested in.