All of your personal information is stored at the my.snu. portal. You can find information about your tuition payment, academic status or run the graduation simulator which will let you know what more classes you need to take.
You can also print certificates for attendance and grades transcripts from there.
Moreover, it is essential for registering for the dormitory, since all of your bills have to be printed from there. After completing your semester, you are required to do a course evaluation in the my.snu. portal in order to get access to your grades.