The purpose of a greeting won't be understood in a literal translation of its words. More often than not, greetings phrased as questions are rhetorical. The real purpose of the greeting is to make contact, for the purpose of establishing a shared atmosphere for the continuance or inhibition of further exchange.
As such, greetings and the set of typical replies are in actuality a dance; it's a two-way communication that involves much more information than merely the words spoken. Inflection, eye contact, and other body language impart valuable cues as to the emotional mindset and level of comfort of both participants in the exchange; the way the greeting is delivered can suggest attitudes that run the gamut from flirtation to hostility.
Typical greetings are:
Each of these has a set of common
responses, which tend to be
neutral:
There is an implicit protocol underlying greetings. The fact that greetings such as "how are you?" may either be answered literally, or with a similar greeting, such as "what's up?", reflects the implicit choices made by both participants whether or not to continue the exchange. Furthermore, replies to greetings are neutral because, otherwise, the reply itself would have to be taken as an attempt to communicate further. For example, if the answer to the question, "how are you?" is "I feel great!", then that reply begs the first person to explore further. Neutral responses are important because they allow both people to probe whether continued conversation is desired on both parts.
The importance of greetings is reflected in the fact that common greetings often comprise the first lesson in a foreign language class or tutorial. Communication is difficult without the grasp and execution of appropriate greetings and responses. Often, humans become annoyed or agitated if either a person fails to reply to a greeting, or communication begins without a greeting. Also difficult is when a person offers inappropriate responses or fails to take cues that no further conversation is desired; these all reflect a failure to negotiate the implied rules of the greeting protocol.