This brass hunting horn belongs to the Traenetreckers, a mercenary corps that is ill reputed for having lycanthropes in its ranks.
As an action, you can play the horn to produce a wolf’s howl that can be heard up to 1 mile away. As part of the same action, you can summon two dire wolves (see the Monster Manual for statistics), as if you had cast the conjure animals spell. Once you summon the dire wolves, you can’t do so again until the next dawn.