Create custom collections in Books on Mac
You can create custom collections to organize items in your library. A custom collection can include books, audiobooks, series, samples, and PDFs.
Create a custom collection
Go to the Books app
on your Mac.Click New Collection below My Collections in the sidebar, or choose File > New Collection.
Enter a name, then press Return.
Add books and audiobooks to a custom collection
Go to the Books app
on your Mac.Click a collection below Library in the sidebar.
Select one or more items, then drag them to any of the custom collections below My Collections in the sidebar.
Tip: To select multiple items, press and hold the Command key, then click the items.
You can also click 
below an item, choose Add to Collection, then choose a collection.
Rename a custom collection
Go to the Books app
on your Mac.Control-click a collection below My Collections in the sidebar, then choose Rename.
Enter a new name, then press the Return key.
Delete a custom collection
Go to the Books app
on your Mac.Control-click a collection below My Collections in the sidebar, then choose Delete.
Note: Deleting a collection doesn’t delete the books or audiobooks in the collection; they’re still in your library.