Char-cloth is made from cotton material (scrap fabric, old undershirt material, rags, etc.) that has been wrapped in aluminum foil and put beneath a fire. As the fire burns and the the coals drop onto the foil, and the material inside chars.
It’s used with a spark striker and dry kindling (jute twine, pine needles, dryer lint, whatever) to start fires. The char cloth catches the spark and burns, lighting small tinder, small twigs, larger twigs, and upward in size until you have a nice, roaring fire.
Then, soon after, s’mores.