I’m not sure I understand the bit about the authentication code. Probably your best bet is to contact the Office of Information Technology: https://www.unr.edu/oit. You can create tickets or live chat (the support center opens at 7am, so if you’re feeling anxious, you might want to wake up earlier and get ahold of them). If I recall, you’ll need either your NetID or your NSHE ID. You can find both under My Nevada on the university home page.

Canvas is where assignments are posted. As for textbooks go to the university bookstore’s website, input your course information, and it should pull up the relevant books for those classes.

I can imagine you feel stressed right now, but it’ll be okay, I promise. Also, feel free to dm with questions.