The nearest 2-12 undead of Hit Dice equal to or less than the level of the caster, and within 100 feet per level of the wizard, travel to the summoner at normal pace. The summoned undead are not hostile, nor are they under the control of the summoner. They may act as they wish.
Once they have reached the summoner, the undead may turn around and go back where they came from, attack anyone in their way, talk to the summoner, or perform any other action that seems reasonable to them. Unthinking undead (such as zombies and skeletons) with a purpose immediately return to their station. Wandering unthinking undead stay and wait for orders (for which the caster needs charm undead, a potion of undead control, or something similar) unless there are obvious foes besides the summoner to attack.
The material component is bone dust, which is scattered to the wind during the casting.
Notes: Common for necromancers of the Red Wizards of Thay, but not taught to conjurers.