"Was darf es denn sein?"
"Was darf es denn sein?". Why does it mean "What would you like to order?", I can not get the idea only from these 5 German words. Does this sentence have any stories, or it's just a fixed usage, such as "wie geht's"?

Thank you.

Question

"Was darf es denn sein?"
"Was darf es denn sein?". Why does it mean "What would you like to order?", I can not get the idea only from these 5 German words. Does this sentence have any stories, or it's just a fixed usage, such as "wie geht's"?

Thank you.

Answer

It is a polite way to ask what they can serve you.

"Was darf es sein?" - "es" is referring to e.g. the food you want to have. So it is basically like asking "What will you have?" in English.

Answer

I agree completely with the first poster. 
I would say there is an implied meaning behind it. 
If you say "Was darf es denn sein"?
Literally it would mean something like.
 "What is it allowed to be? 
The implied thing would mean something like:
"What (food, drinks) would be ok for me to bring you."