The fibres from plants are extracted from the rest of the plant material. They are then mixed up into a tangle and flattened into thin sheets. All this is sounds easy, but requires a lot of knowledge and skill. The process involves several distinct stages.
Choose suitable plants ~ grass ~ flax ~ cotton ~ hemp ~ bamboo ~ and treat them to reduce them to as fine a set of fibres as possible.
Mix the fibres with water ~ and maybe other additives ~ and clean them, removing impurities ~ until a furnish of the right consistency is obtained.
Using a large flat seive ~ a deckle ~ scoop-up a puddle of furnish.
Spread the furnish evenly over the mesh of the deckle, ensuring the fibres are well entwined.
The amount of furnish in the deckle will determine the finished weight of the paper.
Lift up the seive and drain much of the water through it.
Once the mass of fibres has firmed up, remove the sheets, carefully, and gently lay it onto a blanket ~ couching.
Cover the sheet with another blanket.
Scoop up another deckle-full of fibres, and repeat many times, building up a pile of paper-blanket-sandwiches.
Press the pile of blankets and paper sheets. A lot of pressure is required. A hydraulic pump ~ such as a car jack ~ is used for this.
As the excess moisture is squeezed out the weave of the blanket leaves a smooth or rough impression on the paper. The final surface of the paper is determined by the rougness of the blanket. If smooth hot rollers are used the surface will be called Hot Pressed. If no smooth rollers are used then it is Cold Pressed or for short NOT pressed. The word pressed is left out,and the word NOT fully captialized in order to distinguish it from the normal use of the word 'not'. The use of heated rollers, I presume, takes the process away from the realm of being Hand Made
The paper is now ready to dry. Hanging up in a gentle airflow is best ~ air drying ~ on a clothes-line arrangement.
When dry the paper is ready for use. The surface will remain rather too rough for office use, but with care it may be smooth enough for pen and ink. Artist's find it suits their needs for watercolour and other media, especially if an extra sizing process treats the surface to better accept their paints.
I look forward to adding some pictures to explain all this better than any words can.