Hello,
My name is (впиши свое имя), I'm 14 and I want to tell you about my life.
I study at school in (свой класс) class and I very like to do it. I have good marks at school, my loved lesson is (свой любимый предмет). I have a lot of friends at school. But I have a lot of friends out of school too. My best friend's name is (имя лучшего друга), she is very sociable like me and we have the same interests. Usually I go walk wit her or with another my friends.
Thats all, I promise you will like my letter to you.
Best wishes,
(твое имя)