How do you say my in korean? explain how you would say it in different situations. (informal and formal).

You can say my in Korean in many ways. You can say 나의 (pronounced as na-eei). If you want to say, for example, this is my pencil, you'll say 이것은 나의 연필이다. This is more a formal way.
But, if it is informal, you can say 내 (pronounced as ne). It is kind of a shortened way of the informal way, 나의.

Serías guapo, i have no idea if this is right or not but i tried 

Students and school are nouns
good luck!