Notebook paper comes from a multi step process of cutting down trees, grounding them into pulp and then manufacturing the substance into dry, usable sheets of paper. Paper also commonly comes from recycled material, like old paper and cardboard.
Paper can be made from a variety of materials, not just trees. Through the centuries, people have made paper from rice, plants, cotton and even clothes. Most of the paper in today's notebooks comes from a mixture of wood pulp and recycled paper.
Lumber yards commonly have wood that is unusable for manufacturing and other purposes. These spare wood parts are commonly grounded into wood chips where they are then placed into what are called "pulp digesters." These machines break down the wood bits using a combination of steam and powerful chemicals. The wood subsequently becomes a pulpy mass of fiber. The pulp then goes through multiple stages of cleansing, where wood resin, lining, miscellaneous bits and chemicals are removed to purify the mixture.
Another machine then takes the pulp and sprays it onto a wire screen. Wire screens can be huge, with some being 20 feet wide, and they can travel at speeds up to 60 miles per hour, being designed from mass production. The machine drains the water from the thin sheets of pulp, allowing the cellulose fibers in the pulp to dry together, forming paper. It is then heated, pressed, dried, cut and then manufactured and packaged into paper products, like notebooks.