How do you do?
Should I answer the question "How do you do?" or maybe it equals "Hello" and answer not necessary?- Excuse me, Hello!
- How do you do?
and then, should I respond or it is better to ignore this greeting question and continue:
- Could you tell me where is post office situated?

Question

How do you do?
Should I answer the question "How do you do?" or maybe it equals "Hello" and answer not necessary?- Excuse me, Hello!
- How do you do?
and then, should I respond or it is better to ignore this greeting question and continue:
- Could you tell me where is post office situated?

Answer

as I learned, "how do you do." isn't actually a question but a form of greetings that in parallel of the word "hello".  As Eliot suggested, simply reply "how do you do." 

However, if it is to be said as an inquiry, it would mean "how are you?"

e.g. "thank God you survived, how do you do?"

:)

Answer

Just say: How do you do?

Answer

The usual reply is: "Fine, thanks.  And yourself?"

When people ask "How do you do?" they don't really want to know the full details.  It's a question asked by strangers, very much a formality.

Answer

how do u do and glad to meet u are phrases that people say when they are introduced.
 if you don't know these phrases you should learn them. people expect you to say them when u are introduced.