Picture 2 - biscuit tin in fireplace with lid and 2 holes for wood gas to escape N.B very important to have holes or it could explode. Also wire wrapped around tin to keep lid on and to remove from fire.
Video shows the woodgas escaping and being burnt off. charcoal is made when flames cease to burn, in this case it tuck about 1.5 hours Remove from fire and seal holes with sand or mud to prevent the charcoal reigniting.
Simply grind up to the required size.