Once upon a time, kiddies, there was a book published every year whose title was Books In Print (it still is printed, evidently, though I can hardly imagine who would buy it now). It included what it said on the cover -- the publication information for every book in the USA whose publisher had print copies available. If you wanted to track down a book for library use, or to order a copy of your own, you would go to Books In Print, find it by title or author, write down the publication information, and convey that data to a librarian or bookseller.
As a college student -- and a regular reader -- I recall my nearly-weekly trek to the college library in order to retrieve this unwieldy volume from the shelf in the reference section. Before the days of digital databases and Amazon and WorldCat, it may defy the imagination, but this is how I found my books. The idea of having to go someplace and look something up in Books In Print (regular people didn't ordinarily own copies, in my experience) rather than just looking at Amazon or WorldCat seems bizarre. And writing down publication data and carrying it, or mailing it, to the person from whom you wanted a copy ...
Well, that just seems insane.
Yet, that's how it worked back in my day.
Sometimes, I'm amazed we managed to read as much as we did. But we also didn't have Facebook and Google to distract us.