I dont think you understood me my friend. You use ritual skill to revive you`re own undead units. It acts like sacrifice spell : you kill some enemy stack, lets say bowman, and use ritual skill on their corpse then you left click on your own undead units (must be humanoid undead unit), so you cant use it to create new units under your controll on battle field. You must to already HAVE that type of units in army. So to sum it up, you cant use ritual skill if you dont have undead unit in you`re army. To use this skill you have to use 1 type of undead units in 1 of 5 unit slots (so if you use priest, bowman, swordman, archmage, griffin this skill wont do a thing, but if you have zombies instead swordman you can use it to revive you`re zombies from enemy humanoid corpses).

ok i understand thanks my friend to explain

bye