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