Write down your original intention of joining the Student Union Liaison Department (mainly your interest in the Student Union Liaison Department and what you want to learn).

Then there is personal information (hobbies, etc. It doesn't matter if you write something special about the work of the Student Union Liaison Department)

Finally, I wrote that I really want to join, hoping to give me a chance (and I also made a promise that I will work hard if I join the student union's outreach department)

The order can also be adjusted. Wish you success!