It is generally accepted that paper is a thin and fairly flexible substance. Paintings on cave walls in various parts of the World do not count ~ some are exceptionally ancient and worth more study if you are interested. The earliest evidence of writing on flat materials is of documents made and written in Egypt some 5000 years ago. These Egyptian papers were made from the fibres of the stems of papyrus plants. These are tall, strong, reeds that are plentiful in the Nile regions. The fibres were flattened, crushed together and dried out. This ~ parchment ~ was fairly brittle, and had to be handled ~ and stored ~ carefully. Loose sheets were bundled together at a conveient size, or if a long document required that the text was kept in order they were joined and rolled into scrolls.
Fragments of paper have been found in China and dated to around 4000 years ago. They used finer fibred materials ~ wood ~ grass ~ which, as in modern methods of papermaking, were pulped and dried after being laid out in flat and thin sheets. Japan ~ Nepal ~ India ~ and other Asian countries have similar traditions of fine papers from shrubs ~ grasses and trees. See notes on Washi , Lokta  and Khadi .
As the importance of written records became appreciated so new materials came into use. These were principally animal skins such as parchment ~ mainly from sheep ~ goat ~ and cow skins. Smaller animals ~ lamb ~ young calf ~ gave better quality material ~ vellum. These carefully prepared skins were smoother than papyrus, and could be folded. Hence the concept of the codex came into being, whereby a folded sheet ~ a folio ~ could be attached ~ sewn ~ or tucked in ~ to other folios ~ then called sections ~ to make books. (Sections tend to be called signatures in some countries.)
Modern methods of making parchment are similar to the original techniques, requiring the skin to be cured ~ laboriously thinned by scraping-away unwanted tissue ~ stretched ~ and dried. Parchment is extremely durable as numerous thousand-year old documents attest ~ The Lindisfarne Gospels (715) ~ The Book of Kells (800) ~ St Cuthbert's Gospel (of St John)  ~ important UK parliamentary documents are, to this day, written on parchment before archiving. Occasional moves towards economy in this area ~ by using paper ~ have not been fruitful ~ such is the proven longevity of parchment ~ and adherence to tradition.
The method of making paper from fibres involve ~ choosing suitable fibres ~ softening them by boiling and bashing ~ washing waste materials away ~ mixing to a mush (furnish) ~ spreading this sloppy paste-like material our into thin sheets ~ laying them between blankets (couching) ~ pressing them ~ drying them ~ maybe even polishing them (calendering).
This process, essentially that of separating and rearranging the plant's cellulose fibres, is carried out by huge machines ~ the size of football pitches ~ or by artisan papermakers. They use heavy rollers ~ sometimes powered by a water wheel as in a flour mill ~ to crush the fibres. After this most of the work is done by the eyes, hands and arms of experienced workers. We describe this art in more detail