Click on the animals to exert your will, but conserve your power until you grow stronger.
This is samme's entry for Finally Finish Something 2018 and it's really quite captivating! Use the cursors to move the lich around and click the animals to align them with you. They'll then run off and dispatch of the nearest human they can find. Chickens will peck them to death, etc. Once dead you gain their soul, which gives you more power and the ability to capture bigger animals.
And you'll need them, because the more you explore the map, the harder humans you find. Soldiers, knights and wizards can mow through your chickens, and you if they get close enough. So it's a fine balance of dominating and expanding.