Tinder was made of fungus growing on the trunks of trees. It was dried, soaked in salpeter and cut in rectangular, rather short pieces, each meant to be used for one shot only. This piece of tinder was put in the small head of the matchholder; with 15th to mid-16th century guns, the heads of their matchholders were actually too tiny to receive the rather thick matchcord.
The tinder was lit by means of a piece of glowing coal or smoldering match.
If I may direct you to
you will see a piece of tinder in the head of the matchholder of an early 15th century gun.
I have to say that exchanging opinions with you is much fun, thank you for keeping me going.