Those of us who work as writers and editors know how much work goes on to prepare a manuscript for publication. But that's only part of the whole process. There's further work done within a publishing house, including more editing, cover art, marketing, and sales, just to mention a few areas. The material is prepared for the printer, these days, digitally, where it goes through a sequence of pre-press preparation, printing, collating, binding, packaging, and shipping.
Here's a look at how a book is physically put together by a printer here (created for Webcrafters Inc. in Madison, Wisconsin).