This section is for managing your library of authors and books.
If you add an individual book, and select "None" for the metadata profile, only that book will show up under the author when it's added. If you want other books for that author added, choose an appropriate metadata profile.
The Sort and Filter options are the same here as the main Library screen and are documented above.
After selecting the authors you want to make mass changes to (you can select, and shift-click further down to select an entire range), you can make changes to monitoring status, quality profile, root folder (do not change this if you use Calibre), rename files (do not change this if you use Calibre), write metadata tags, set Readarr tags, or delete authors by clicking on the correct option at the bottom of the screen.
The Filter options are the same here as the main Library screen and are documented above.
Here you can do mass updating of the monitored state of individual books as well as authors. A solid flag indicates monitored, and an outline indicates unmonitored.
If there are books listed here, then they are unrecognized by Readarr and are not listed as "existing" in Readarr, but they are in one of the root folders you've defined.
You can get more info by clicking on the i icon on the right.
You can manually import the book by clicking on the person icon on the right.
You can delete the book file by clicking on the trashcan icon on the right.
You can also click on Add Missing at the top to try to add all books to Readarr. Note that this can be time-intensive if you have a lot of books listed here.