Books are a tricky thing. There are a ton of variables. Are these books from the store? ...and are you in Education?
If the first answer is 'no,' then just host or add to your distribution point and set it to 'install automatically/prompt user to install.'
If 'yes,' then if you are in education, you can automatically assign Books to managed Apple IDs that come from the same Apple School Manager ORG. Once this is done, users simply need to sign into Books on their device (iOS or macOS) and the books will be in their library.
Things get more complicated for non-EDU, as you have to deal with end users and their personal Apple IDs. They will need to accept a VPP invitation from your ORG before books can be assigned to them.
