"Most medieval manuscripts were written on specially treated animal skins, called parchment or vellum (paper did not become common in Europe until around 1450)." Source: The Getty Museum.
"... After the surface had been prepared, the parchment was ruled, usually with leadpoint or colored ink ... The scribe wrote with a quill pen made from the feather of a goose or swan. The end of the feather was cut to form the writing nib. A slit cut into the middle of the nib allowed the ink to flow smoothly to the tip of the pen. The appearance of the script—whether rounded or angular, dense or open—was partly dependent upon the shape and the angle of the nib."
"... Once the writing and illuminating had been completed, the parchment sheets were folded and nested into groups called gatherings. The gatherings were ordered in their proper sequence and sewn together onto cords or leather thongs that served as supports. Once the sewing was finished, the ends of the supports were laced through channels carved into the wooden boards that formed the front and back covers of the book. The binding was usually then covered in leather or a decorative fabric."