Question

written an application to your principal for granting leave for five days due to the marrige ceremony of your elder sister

Answer 1

I hope you know the format of a formal letter. You can just use whatever format your teacher taught you because it may vary from place to place. That being said, you can write the following as the body of the letter:

I am a student studying 10th ( it whatever class you want) standard in (your school name). My elder sister, (name), is getting married at (venue) in ( city name) this Saturday, (date). Since it is a huge event in our household, my family and I will be constantly engaged with the wedding preparations. Therefore, I kindly request you to grant me five days of leave,from (date to date) to attend the joyous occasion . Thank you.