Flint is an item used to craft basic tools. It can be found on the ground or by mining smooth or gold veined Boulders with the Pickaxe. Flint is not flammable and easy to find on the surface, although eventually it can be used up. More can be found by venturing into a Cave, however.
Flint is one of the first and most needed items in the game and should be sought after as soon as a new game starts. It is recommended to always have at least 2 flints at all times for cases you need to make a basic tool or Spear.