Generally, people only ask "How do you do?" the first time they are introduced to someone. It's a little more formal than "How are you?". "How are you?" can be used anytime as a greeting or as a way to inquire about someone's health. I hope this helps.

the two words both are greeting`` 1.'how do you do ' is for the first met strangers, 2, 'how are you' is for acquaintances` , but meaning is the same` now, most people use' how are you ` i think 'how do you do' is already outdated

Benjamin is right. "How do you do" is rarely heard these days. I would never use it when being introduced to anyone. I would say "nice to meet you" or if addressing a woman, probably, "a pleasure to meet you." "How are you?" and "how are you doing?" are pretty much the same. A much more informal way of saying this is "how's it going?".

How do you do? This is not a question. It is another, very formal way of saying "Hello." It is also very British. The correct response is; "Pleased to meet you." or "How do you do." or just "Hello." We only really use it the first time we meet someone. How are you? This is a question, but the person asking it doesn't really want to know the truth about your aching back or hangover. A polite response is; "I'm fine thanks. And you?"

Thanks for your comment. Very interesting.