One possible version:

Dear Sir/ Madam,

        I hear the Chinese and American Students' Summer Camp will be held in Hawaii. I am interested in this

summer camp and hope to join in. I am a 15-year-old Chinese middle school student. I am learning in Beijing

No. 36 Middle School. English is my favorite subject. I also do well in other subjects. I like reading and often

go swimming in my school's swimming pool. 

        I would like to join the summer camp because I want to improve my English by practising it with

American students. To know more about different people and countries will be good for my language study.

I am sure I will make a lot of friends there. Seeing the good scenery in Hawaii is my dream from the childhood.

        Hope I can get the chance.