Yuto's Quirk, in theory, works as a weapon materialization ability for combat.
In reality, it is far more complicated than that.
First, he cannot summon any weapon he wants. He can only summon weapons related to each of the individuals living inside his mind. Therefore:
Simo Häyhä – Mosin–Nagant M28/30
Jack – Gloves
Tesla – Bomb-based armor
Adam – Brass knuckles
Qin Shi Huang – The most versatile (sword, spear, halberd, crossbow, and armor)
Alexander the Great – Xiphos sword and bronze shield
Baldwin IV – Crown (the most dangerous one)
Second: the original wielder must agree to grant Yuto access to their weapons. Otherwise, he cannot summon them.
Third: There is a second stage of the Quirk called Possession. It occurs when Yuto voluntarily allows any of the seven to take control of his body.
Possession can also occur involuntarily, but only if two conditions are met. The first is Yuto's inability to resist, meaning he must be in an unconscious state. The second is that all seven individuals must agree on who will take control of the body.
That should provide a solid foundation for understanding the protagonist and his Quirk. The rest can only be discovered by reading the story.
Anyway, enjoy the reading.