Using "¿qué? and ¿cuál? in interrogative sentences; You know them better as "questions".

Asking “How Are You?”

Read the following dialogue between Marcos and Ana. 

Marcos: Hola, Ana.  Hello, Ana.

Ana: ¡Hola Marcos!  Hello Marcos!

Marcos: ¿Cómo estás?  How are you?

Ana:  Bien, ¿y tú?  Good, and you?

Marcos:  ¡Bien, gracias!  Good, thanks!

Above, notice how Ana referred back to Marcos using tú.  Marcos also asked Ana how she was doing using the tú conjugation of the verb estar (to be).    

If the two persons in the dialogue don’t know each other and some formality is expected, the conversation would go like this:

Sr. Cruz:  Hola, Sr.  ¿Cómo está Ud.?  Hello, sir.  How are you?

Sr. López:  Muy bien.  ¿Y Ud.?  Very well.  And you?

Sr. Cruz:  Muy bien.  ¡Muchísimas gracias!  Very well.  Thanks so much!

Notice the subtle change of the conjugation of the verb estar, from estás to está.   This is important so the conjugation of the verb fits the subject pronoun of the sentence, whether it is tú or Ud.