To obtain this achievement you'll need 3 items:
x1 Flint (found in camps)
x1 old lumber (found in lootable structures, hardware stores for sure)
x1 tinder (created with x1 cattail)
combine those together to create a campfire which goes into your inventory. Place it and then it is ready for use. can't remember if the achievement popped when it was created or when it was placed. Either way most likely one of the first achievements you'll get in the game.