“Hi, How are you?”: Greetings in the United States
Americans greet each other in specific ways that, as you may have noticed, might differ from your home culture.
Firstly, Americans always say “Hi, how are you?” and generally don’t wait for an answer as they continue walking past someone. Meanwhile, the other person is responding, “Good, how are you?” while they continue walking, too. You are not even required to answer, considering that the other person may not hear you since you’re both walking away.
If you are still wondering what all this means, the question “how are you?” (or “how’s it going?”) just simply means “hello” and is meant as a greeting. There is no expectation for an answer. In fact, it would be odd if someone were to say anything more than just “Good” or “Fine.” Don’t take it personally. The person who really wants to know how you are doing will still greet you in the same way, but they will also follow up with “So how are you doing?” and actually pause for an answer.
“Hey, what’s up?” You must have been greeted by this phrase, but do you know how to respond? In fact, “What’s up?” or “What’s going on?” is typically used in a phatic manner as opposed to actually being a question with an expectation of an answer. The purpose of this phrase is to indicate interest in the other person. Because of this, “Nothing much” is a perfectly valid response. If this sounds boring, you can try one of the variations like, “Same old, same old.” Check out the discussion about “What’s up” at StackExchange Interpersonal Skills.
Learn how to respond to other conversation starters.
When Americans first meet each other, a firm handshake with eye contact is expected. If you have a weak handshake, Americans might assume you are shy, and if you don’t have eye contact, they might suspect you have something to hide.
After Americans have met someone already (this could even be the day they first meet) it is acceptable to give a polite hug goodbye, and the next time the American sees this person, they will probably give them a quick hug hello. This is usually reserved for peers and friends, however (not professors and bosses).
Nowadays, you’ll see some Americans giving fist bumps in place of a handshake or high five (stereotypically, these are American males). Some people might choose to do a fist bump to try to avoid germs.
Source: Etiquette in US – How People Greet, Gestures, Thank you, Sorry?