---"¿Qué tal?" -> it sound more like the typical phrase you say like "hey", "okay", "hi". ---"¿Qué tal estás?" -> it is a bit more serious, just a bit. In this one you show more interest about how he/she is instead of just saying something greeting When you answer someone's "¿qué tal?" or "¿qué tal estás?" you can ask him/her as well and easier by asking "¿y tú?". Anyways you can say too "¿qué pasaaaaaaaa?". It is like the Spanish "wazzup!!!"

How are you? = ¿Cómo estás?

¿Cómo te va?

¿Qué tal?

How are you?= cómo estas?, qué tal te va?, cómo te va? I think that this are more equal in your language.