Guatemala has many many typical Spanish expressions, some of them are quite unique to Guatemalans and other are part of the language culture across Latin America, and ¿Que manda?... or Mande? Is one of those Spanish expressions you should learn about.

Both ¿Que manda? and ¿Mande? expressions mean exactly the same… you could use either one, but of course since ‘¿Mande?’ is shorter, it is used in Guatemala when there is no need of much conversation.
Depending on the situation, this expression means ‘What did you say?... what can I do for you?... What do you need?...

Technically, the word ‘manda or mande’ comes from the Spanish word ‘mandar’ or ‘mando’, which is translated as ‘command, instruct or order’... but the Spanish Language culture around this expression has given a different concept to it , so you cannot say ‘What is your order?... What are your instructions?... or even ‘What is your command?’ to say the same thing, for those literally translated in Spanish would be like : ‘¿Cual es su orden? or ¿Cuales son sus instrucciones?. These sound somewhat imperative, while the actual ‘¿Que manda?’ expression is more polite and shows respect.

Something important to understand about this expression is that you can only use it with someone either superior to you, like your parents, professor, a customer or your boss, or someone that is at your same level, but also you have a good relationship with, just like a brother / sister or a friend. 

Lets have two basic examples to understand and apply these expressions:
¿Que manda?...
Let's say that you heard your father calling you up from down stairs, but you are not so sure of what he said, so your answer is ‘¡¿Que manda?!’... as meaning, What did you say?...or did you call me?.
Now… you can add a ‘subject’ in this expression to make emphasis in your response to that someone, like ‘¿Que manda mamá? (to your mother)... or ¿Que manda señor? (to your boss at work).

Mande?...
Let's pretend that you are at work and receive a phone call from you sister, and you answer saying ‘Mande?’... as meaning : What can I do for you?... the situation requires a short conversation since you are at work and can’t speak for long.

EXTRA NOTE : In the old days, when answering a phone call, instead of saying ‘Aló’ like we usually do today in Spanish, people used to say ‘¿Que manda?’.

So now you know and try to apply it yourself !!