>>33377951
A "blue book" is a few pieces of lined paper stapled together inside a blue paper cover and sold at your bookstore. You use them for essay-based exams. I usually buy them for my students, because, if I don't, they'll fuck up and not come to the exam with one. They're much easier than dealing with sheaves of loose paper or something torn out of a notebook.
Students also write much better essays by hand than they do on computers. They can't think with a delete key offering them the chance to un-commit to something. Once they're forced to commit to an idea that they've started, they can usually come up with something reasonable to say.