1. "How are you?"
2. "How have you been?"
Every student of English knows the answer to the first question ("I'm fine." / "Not bad." / "Great!"/ etc.) It is a simple exchange in the present moment.
But if I ask you, "How've you been?", I am inviting you to describe your life SINCE THE LAST TIME WE SPOKE. Using the Present Perfect tense, I am referring to the time in your recent past UP UNTIL the present moment. So you might describe what you HAVE BEEN doing at work, events in your personal life, or your health - whatever you want to share from your life.
The second question is thus a "real" question, that is, a request for real information, whereas the first question is usually just a routine exchange. Often native speakers will begin a conversation with a "How are you?" only to follow it up with "How've you been?" when further information is desired.