Honor points are points that you can obtain through attacking other players with honor points that you can steal. If you lose an attack then you get no honor points. If you lose a battle at your castle you lose honor points. Occasionally if you attack somebody that is too low a level, you will lose some honor points of your own. This is to prevent players from farming low levels
At the beginning of the game, it is possible to obtain honor points by attacking other players with no honor points. Honor points affect your ranking where you can gain weekly prizes depending on the number of honor points you have. For level 70s, they can attack as low as L45 and not lose any honor.