You fire a piece of nonmagical ammunition from a ranged weapon or throw a nonmagical weapon into the air and choose a point within range. Hundreds of duplicates of the ammunition or weapon fall in a volley from above and then disappear. Each creature in a 40-foot-radius, 20-foot-high cylinder centered on that point must make a Dexterity saving throw. A creature takes 8d8 damage on a failed save, or half as much damage on a successful one. The damage type is the same as that of the ammunition or weapon.
You can find more information on this spell in: PHB.226