As long as there is no class in the classroom, you can basically go in for self-study. However, it is recommended to go to the science building to find a classroom for self-study. There are many large classrooms, many people studying and a good environment, which is suitable for self-study. There are many idle people in the teaching building, and the environment is noisy.
You don't have a library card, because you are not a student of normal college. You can't borrow books without a library card, so you can only borrow them from classmates you know. If you want to read periodicals and magazines, you can go to the current publication room of the library and just go in without the librarian.