In this image you can see the charred tinder in the tinderbox. Sparks are struck from the steel with a piece of flint or similar rock directly onto the tinder in the tinderbox.
Here you can see two different plant tinders, the top piece is a bracket fungus, the lower two pieces are Punkwood/Punk wood.
Although technically Punk wood is wood, it is a special kind of wood. It is dry-rot wood, very soft to the touch with a spongy feeling. NOT just any piece of wood will do, it must be Punk wood. Punk wood is usually found in the base of fallen trees.
In this image I have turned the plant tinder upside down so that you can see that the tinder is not charred right through, only the outside is charred, and in this case I have only charred one side completely. As you use the tinder in your tinderbox it will continue to char itself, AND it will char any uncharred tinder that you may add to the tinderbox.
Charcoal will not work in the sense that the charcoal is charred ordinary wood. If you use anything other than properly prepared plant tinder in your tinderbox you are doomed to failure, and this can be dangerous in a survival situation.