The big idea
Instead of copying a book by hand, letter by letter, the printer makes many small metal letters that can be arranged into a page, inked and pressed onto paper again and again. A screw turned by a long bar gives the hard, even push that prints the whole page at once. When the run is done, the same letters are taken apart and set into the next page.
Memory trick: “Cast it, set it, ink it, press it.”
A bit of history: Johannes Gutenberg was born in Mainz, in Germany, around 1400; the exact year is not known. Records place him in Strasbourg in the 1430s, where a lawsuit in 1439 shows he was working on a secret invention and that a carpenter had been paid to build a wooden press. Back in Mainz around 1450, with money borrowed from Johann Fust, he was printing with metal type, an oil-based ink and a press probably adapted from those used for wine, oil or paper. His great work, the 42-line Bible in Latin, was probably begun soon after 1450 and finished in 1454 or 1455: in March 1455 the future Pope Pius II wrote that he had seen pages of it at Frankfurt. About 160 to 180 copies were printed, most on paper and the rest on vellum, and 49 survive at least in part. Movable metal type had already been used in Korea, but Gutenberg's system of type, ink and press spread across Europe within a few decades. He died in Mainz, probably in 1468.
Long before printing, Job wished his words could be kept for ever: Oh that my words were now written! oh that they were printed in a book!
(Job 19:23, KJV)