que tal? what does it mean and how to respond
Like most salutations they can be either an actual query or a rhetorical question.
What more interesting than its use by itself is its use given in our dictionary:
¿qué tal…? -> how…?
¿qué tal (estás)? -> how's it going?, how are you doing?
¿qué tal el viaje? -> how was the journey?
see the first link for more examples of this usage.