Learn English – “How are you” in America

Here are a few ideas.

Casual non-acquaintance:

 - Hi.
 - Hey.
 - How are you?
 - How are you doing?

Formal (to whatever level above you that requires some measure of obsequiousness)

 - Good morning.
 - Good afternoon.
 - Good evening.
 - Hello.
 - Nice to meet you.
 - How are you?

Informal (to friends)

 - Hey!
 - Sup?
 - Dude.
 - What up?

And so on. You almost never say "How are you?" to your friends, unless they've been ill or away and you have a legitimate reason for wondering about their health.

As for different tones:

How are you?

Can mean either indifference or extreme interest. Look at the person's face and decide for yourself. If you're in the hospital it signifies interest. If at a fund-raiser for a political candidate, not so much.

How are you ?

Indicates a sudden focus of attention on you, as if you were The Most Interesting Man in The World or someone knows and likes you but hasn't seen you for a while.

How are you?

Indicates a correction to your misunderstanding of the unstressed "How are you?" in which you thought the person was asking "Who are you?"

Yes. Depending on where you are in the English-speaking world and on your relationship with the other person, you might reply with any of the following:

• I'm fine, thank you.
• I'm good. You?
• Doing great! And how are you?
• Good. Doing okay?

Certainly, several other possible permutations. No response at all would be considered rude anywhere. Just saying, "Fine," in response without a "thank you" or a reciprocal question would also be considered brusque, standoffish or rude; or the asker may simply conclude you are in a bad mood. The first response is the norm in places or cases where the respondent does not deem it polite or appropriate to respond in kind with a "How are you?"