This link is one of my favorite for explaining right of way to people (note that the NH rule book makes mention of "right of way" though there is truly no such thing when each boat has a duty):
http://www.navcen.uscg.gov/mwv/navrules/Arcs.htm
If a boat is approaching you in your "
green" zone, then you are the give way vessel because the other boat has the green light to go (and therefore it must maintain course and speed).
Likewise, if a boat is in your "
red" zone, it has the red light and must give way to you. You are then the stand-on boat and must maintain course and speed.
If a boat is approaching you from the remaining arc (encompasing the stern light in the diagram), then you are being overtaken. In an overtaking situation, the boat being passed must maintain course and speed (stand-on); the boat doing the overtaking must give way.
Hope that helps.