iMore put together a great guide for iOS 12 Apple Books. It covers everything from book samples, downloading/highlighting, PDFs, audiobooks, and more.
Apple Books will now automatically organize your library into several collections, and you can add as many of your own as you wish. In addition to books and audiobooks, you can store PDF files in the app—and all of it can sync among your Apple devices through iCloud.
As you may have known, I’m a big fan of the new Apple Books app and I hope Apple continues to improve it.
Check It Out: The Ultimate Guide to iOS 12 Apple Books