When a book is bound (properly) large sheets are printed with the pages, these are then folded and stitched, - I think it may be 8 at a time, finally the edges are guided/ trimmed so that the pages are separate.
Cheap paperbacks are usually gummed I think but this applies to hard backs and the “better” editions of soft backs.
You could Google it.
“The sheets are folded down to make a “gathering.” In earlier times, printers and binders often did not trim the edges, choosing to issue their books with the edges uncut and the gatherings unopened (the Spanish term for this is intonso)..”