Tinder is essential for igniting a new flame; without it, creating fire is difficult. They used tinder to quickly start the bonfire.
Pro Tip 2/3
Survival Skill
Knowing how to find and use tinder is a valuable skill in wilderness survival. Survival training taught her to identify good tinder in the wet forest.
Pro Tip 3/3
Not Literally Trees
The word 'trees' in this context refers to the bark or small parts, not the entire tree. He scraped tinder from the tree's bark, not from the tree itself.