Charcloth is used to aid in the lighting of fires. It is made from cloth, such as linen, that has been charred or burnt. The method to make charcloth is fairly simple. You either place small pieces of cloth in a metal tin, or in a pot and then cover with sand. You add this to a fire so that the cloth heats up and start to smoulder. The aim is to pre-burn your cloth. Once the holder you have the cloth in has been added to a fire you wait for it to start smoking, this is the cloth inside burning, after a while remove the pot or tin from the fire and check the cloth. Ideally it should have turned black. It will be fairly fragile, if it hasn’t charred then add it back to the fire and wait a bit longer.
Because it has been pre-burnt a spark will cause it to start smouldering.