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

Both ¿qué? and ¿cuál? mean "what?" in English, but the verbs in Spanish change depending on where they are used.  "cuál" comes before the verb ser for the most part, or it comes before a posted selection.  If before a posted selection, it takes the meaning of the English "which?".  

¿Cuál fue la mejor parte de la película? What was the best part of the movie?

¿Cuál es el día de hoy? What is today's date?, What's today?, or What day is it?

¿Cuál vestido quieres usar, el azul o el blanco? What (which) dress do you want to wear, the blue or white one?

When we want to refer to several objects, we use ¿cuales?.  Since the penultimate syllable is naturally accented here, we drop the diacritical mark, and make ser the third person plural conjugation:

¿Cuales son los restaurantes que a ti te gustan más? What are the restaurants that you enjoy the most? 

Qué is used for only specific grammar utterances when meaning what? We use qué when telling time, saying the date, referring to a specific noun, or asking the general definition of something.  Observe, por favor: 

¿Qué hora es?  What time is it?

¿Qué mochila es la tuya?  What backpack is yours?

¿Qué quieres hacer hoy? What do you want to do today?

¿Qué es Mazatlán? ¿Es el nombre de una ciudad?  What's Mazatlan? Is that the name of a city? 

When you're astounded by something, and you're like "What the heck is that?", you simply use the neuter form of a demonstrative adjective, eso or esos.  Notice that this is emphatically done before the verb ser, unlike previously.  

¿Qué es eso?  What is that? 

¿Qué son esos? What are those?  

Ojalá que te ayude, 

Profesor Joel

A Simple Approach to Asking Questions in Spanish

 You might think that this is a no-brainer.  Asking a question in Spanish is like asking a question in English, except there is an inverted question mark at the beginning of the sentence.  Yes, that is how a question (or, interrogative statement if you want to get technical) is indeed written, yet the way of forming a question in Spanish is much more in the spoken voice.  

In English, we also use our voice to express a question, by a slight inflection at the very end of the question, along with interrogative quiz words like Is", Are? and the 6 other interrogative words we learned in elementary school: who, what, when, where, why, and how.  

Spanish requires the same kind of pattern.  However, there is much more emphasis placed on the final syllables.  It also contains the following interrogatives: 

¿Quién?, or plural ¿Quiénes?  Who?

¿Quiénes son esas muchachas?  Who are those girls?

¿Qué?  What?

¿Qué es paella? ¿Un plato español?  What is paella? A Spanish dish?

¿Cuál? or plural ¿Cuáles? - Which? or Which ones?

¿Cuál es el celular suyo?  Which cell phone is yours?

¿Cómo?  How?

¿Cómo llegaste al aeropuerto? ¿Por taxi?  How did you get to the airport? By taxi?

¿Por qué?  Why?

¿Por qué quieres romper con Ashley?  Why do you want to break up with Ashley?

¿Cuándo?  When?

¿Cuándo es la fiesta?  When is the party?

¿Dónde?  Where?

¿Dónde está Caracas?  Where is Caracas?

¿Adónde?  Where? (when inquiring as to destination) 

¿Adónde vas?  Where are you going to?

Hope this helps!

Joel