I need someone to explain this more clearly

"This arcane blade contains the bound essence of Drach'nyen, a
writhing warp entity that can rend reality apart. The sword makes 1
attack per turn, with no re-rolls. Any hit inflicted ignores armour
saves and kills the victim outright. Vehicles struck by the blade
are penetrated automatically."

i need to know how this auto matic stuff happens and when it happens

(if quoting like that was/is against the rules, my bad)