letter to the dean for an admission

hi Im writing a letter to the dean of the deapartment in order to start a master. the problem is that i dont know how to they say that i have to say the reasons why i want to enroll in the program and why they should take me
this is is for an admission to a cultural master
please help me to write a letter to the dean
im really desperate i dont know how to write it and its urgent
god bless uuuuu
thank you so much