In many cases, a simple "Hello" is a prefect way to greet someone in the US. "Hi" is also a suitable greeting. Both are typically said with a smile or a nod of the head, If you make eye contact with someone within speaking distance, it works as saying "Hello" or "Hi". A less formal greeting is "Hey",though it should not be used in formal social settings. Besides, when some people in the US say "How's it going?", they're most likely just saying "Hi",and not in fact asking you to go into detail about your day. You can answer,"Good, and you?" or "Good, and how about yourself?" Other variations of this greeting include How are you? and "How are you doing?"