Library of Congress Subject Headings are located in almost every single online catalog record, and are located underneath the title and author. These headings collocate all the books are on a specific subject and are hyperlinked, so clicking on each heading takes you to other books that have the same subject. These work a lot like Facebook tags! When some book is "tagged" with a specific subject, the catalog links all the books with the same subject tag together. For example, in the online record for Viewing African Cinema in the Twenty-First Century, there are five subject headings:
Clicking on the first heading, Video recordings -- Social aspects -- Nigeria gives you every book and article tagged with those three phrases. Video recordings industry -- Nigeria will give you results specific to the business side of Nollywood. NUsearch also works like a search engine. This is a great way to browse library materials if you don't know exactly what you're looking for!