Database System exercise. need help

Gemilang Taekwondo Centre is situated in Kuala Terengganu. It teaches students taekwondo and prepare students for 'Belt Grading' examinations. As number of students has increased every year, the top management has decided to build a system to manage and organized all student's information that has registered to the centre. In order for the staff to use the system, they need to access the system using their username and password. They are able to use the system whenever the authentication has been verified. Otherwise, message to indicate invalid user will appear in the screen. When a new student wishes to enrol to the centre, student will be asked for their identification number and make registration for the student. Staff will key in relevant information such as address, contact number, subject request and total fee of the enrolment in the system. Student can enrol based on their previous taekwondo belt grade (if student has previously learned taekwondo) or start from basic class. There are Taeguk 1, Taeguk 2, Taeguk 3, Teaguk 4, Teaguk 5. Teaguk 6, Taeguk 7, Teaguk 8 and Poom Class. However, student can only be enrolled in only 1 class at each time. Each student needs to enrol in a new class after passing belt grading exams. In order to enrol in Taeguk 2 class, student need to pass for Taeguk 1 belt examinations first. It is the same for other belt stages. Students they can withdraw enrolment whenever they like. Once enrolment has been confirmed, the system will generate a bill. Student can collect bill from staff. Draw context diagram and DFD level 0 for the give case study. (20 marks)