In the days before machine looms and store-bought materials, wool was a major source of income, and being able to spin and weave it meant a woman could provide warm clothing for her family. Carding wool is the process by which wool fibers (or cotton, for that matter) are separated and prepared for spinning. It can be done by hand, or nowadays, by machine.
Carding wool by hand takes practice. The carder takes two carding combs, which have upstanding teeth, and loads one with the wool fibers. Using a back and forth motion, the person places one carder on top and "combs" the carder through the wool on the lower carding comb. When all the wool has been transferred from the bottom carder to the top, the carding combs are flipped over and the process is reversed. When the wool is light, airy, the fibers separate and free from tangles, the mass is formed into a rolag, or roll of fiber, for use on a spinning wheel.
Carding wool by machine doesn't take as long, and obviously, more wool can be carded at one time. When carding wool by machine, the operator puts the wool fibers on a drum with very coarse teeth. The wool is then transferred over a series of rolling drums, each with successively finer teeth. When the operator takes the wool off the last drum, it is separated into individual fibers and is ready to go to another machine to be spun into thread. The carding technology has changed little in the past several years, mostly because the drum method is the most efficient way to get large amounts of wool fiber carded and ready for use in garments in a relatively short time.
Many fiber and spinning guilds still teach the carding wool technique by hand. They also teach how the wool can be spun into thread, and even how to weave the thread into cloth. Someone wanting to appreciate the hard work and craftsmanship of a bygone era could begin with learning to card wool and spinning it into thread.