Anything আপনি want... journal entries, taking notes in class, doodling, লেখা stories, songs, অথবা poems, লেখা things down that আপনি don't want to forget, keep track of your পছন্দ quotes, use it to make lists, make paper airplanes... the তালিকা goes on. :)
Maybe a diary, অথবা maybe notes for school অথবা for hobbies like if আপনি write. অথবা maybe আপনি can use it to draw, that's what my cousin does. Just doodle with it. Use it to do your homework on. Anything আপনি want!