Yeah, that one is dumb and i don’t recommend using it. Much better to put together the charcoal kiln from the construction menu instead. To use the metal one: Craft it, then craft again but pick “filled charcoal kiln”. then activate that item to ‘light’ it. drop it on the ground and wait 5 hours. then you can 'a’ctivate it again and it becomes a ‘finished charcoal kiln’, finally pick it up and 'd’isassemble it to get your whopping 40 charcoal. It’s really stupid, don’t use it. If you load up a stone charcoal kiln with logs you can get 2600 coal in 6 hours just by dropping the logs on that space then 'e’xamining it to light it. super easy and you get lots of coal.