Okay is a human more closely related to a cat or a dog? - I don't know, but as a guess I would say humans are more closely related to dogs than to cats. Cats are more specialized carnivores than dogs.
Are you sure we're not related to rocks? Aren't we all stardust? - we aren't related to rocks. The phrase 'related to' makes reproduction necessary. Rocks aren't life-forms and they don't reproduce.