how/where do i buy the aplia access thing if i bought a used textbook for macroecon 1bb3?

I believe you can buy it at Titles, its probably going to look like a piece of cardbored trapped in a plastic security box, which will be taken off once you buy it

My suggestion would be to return that used textbook if you can since purchasing an APLIA code gives you access to the online version of the latest edition textbook.

You can purchase the subscription through the website http://aplia.com/ or buy an access code at the Titles bookstore. First sign up on the site following the instructions on your course syllabus, which is given out on the first day of class. You need a course code which is written on the syllabus as well as to sign up using your MACID so they can identify you. That's all in the syllabus.

Also you are given a grace period of 14 days (maybe longer?) until you actually have to pay/enter in the access code so there's no rush in getting one immediately.

You should return the old one anyways even if you want a hard copy of the book since the cost of a used book and the software will be more than the new book which comes with aplia