Summarize this article in one sentence.
When meeting a royal person, it's important you offer a bow or a curtsy. This is considered a formality, especially when meeting a member of the British royal family.  If you're male, you should do a neck bow. This simply means bowing by nodding your head. If you're female, do a small curtsy. This means dipping your body downward slightly by bending your knees. These are among the highest ranking types of royalty, so be sure to address them properly. Emperors, kings, and queens should all be addressed differently.  When referring to an emperor, you would refer to him or her as "His/Her Imperial Majesty, Emperor of (Name of Country)"; when addressing one, replace "His/Her" with "Your". When referring to a king, say, "His Majesty, the King." When addressing a queen, say, "Your Majesty, my Queen." As these are generally the second highest ranking royals, be sure to address them properly. Princes and princesses must be addressed differently.  For a prince, say, "His Royal Highness, Prince of (Name of Country)." For a princess, say, "Her Royal Highness, Princess of (Name of Country)." There are also formal titles required here. When meeting a duke or a duchess, a formal greeting is necessary.  For a duke, say, "His Grace, the Duke of (Name of Country)." For a duchess, say, "Her Grace, the Duchess of (Name of Country)." There are various other forms of lower ranking royalty, such as barons, knights, marquees, earls, and countesses. There are proper titles for these people as well that must be used when you address them.  Some titles are simple. For example, a knight is simply addressed as "Sir" followed by his name, and a knight's wife is addressed as "Lady," followed by her name. The same is true for baronets and their wives. Royal people that fall between knights and baronets and positions like king and queen are usually addressed as, "The Right Honorable," followed by their name. A marquee, for examples, would be addressed as "The Right Honorable."

Summary:
Give a head bow or a curtsy. Choose the proper greeting for emperors, kings, and queens. Call princes and princesses by the proper title. Select the right term for dukes and duchesses. Make sure you know the proper titles for lower ranking royalty.