In the manga this kid (he was young) was cast out by his family and found this book where he could make people/his own monsters (the people he made could talk and have their own specialties) and he made some teammates like that and one of them was super smart. I think the story was a reincarnation story. It was all black and white and he found the book in, I think, a basement he was locked in or thrown into but I'm not sure. Also, him finding the book was predestined, I think.
"The Black Create Summoner: Revolt of Reincarnated"
Given your description, it might be "黒の創造召喚師―転生者の叛逆" (in romaji, Kuro no Souzou Shoukanshi: Tenseisha no Hangyaku), most of the time translated as "The Black Create Summoner: Revolt of Reincarnated" or "The Black Create Summoner: Revenge of the Reincarnated".
I've put the synopsis down the answer for you to check.
First volume cover
Due to a god's mistake, high schooler Tsuguna died before his time. In exchange, the god agreed to do him a favor in his next life. Tsuguna is reborn to a noble household in a world with magic. He has an unusual form of magic that he requested from the god, the ability to create summoned creatures. However, his dark Japanese hair and eyes mark him as a cursed child in this new world, and his powers are slow to appear. He's kept in a dark basement where he reads his family's books, until one day he finally uncovers the key to his powers. Finally, he can set off into the world with his summoned companion to level up his skills!