Dear (name),
I'm sorry, i couldn't write earlier because i was busy with my exams.
This is to tell you about my school uniform. In my school uniform is obligatory. All students must wear an uniform. For girls it is a skirt or trousers and blouse. For boys it is a costum. Colours of clothes is black and white. Thats all about my uniform.
Well, do drop me a line.
Miss you,
(your name)