What does como es tu mean?

That means "How are you?"

Cómo está means how are you? (formal/familiar) cómo estás means how are you? (informal)

if ser is being used, you would never say cómo es tú because that means how is you.

Rather, you would say cómo eres tú... that's if you are asking how he/she is (describing) like how that person is... an aspect of that person... Like is she tall, blonde, smart, etc.