If he was a feral kitten then yes, he would not know how to use the litterbox.
Especially if mom was not around to show him. :sad:
It is a good idea to give him a small room with his own food, water, bed and toys. The poor baby will be stressed if he is very young and away from all that is familiar.
Here are a couple of sites that may give you some ideas on training.
Once he gets the idea that he needs to use the box it shouldn't take long. I'm really surprised the rescue is adopting out black cats at this time of the year. In this area they refuse to adopt black cats in October. Thank you for adopting him. I'm sure once he figures out what he needs to do he is going to be a super kitty. My black guys are all so lovable.