Arena
The arena has 4 areas. The "big" arena which is used for group training and various team or solo combat activities, the 1v1 arena which has a series of small arenas for 1v1 combat, the Group arena which is used for evenly matched team fights, and the siege equipment training area. Nation points are not earned or lost in the arena.
The arena is the only place where cross faction chat is enabled.
Big Arena
To access the big arena, click the crossed swords icon under the minimap. This is a great place to work with parties, guilds and meet members of enemy nations. Guilds frequently hold training events in the big arena, and the developers occassionally hold 5v5 tournaments here. There is a monument displaying the names of the winners of all the previous tournaments.
1v1 Arena
Queueing up for 1v1 duels is done with the ink and quill icon underneath the minimap. When an opponent is found, you will be teleported to the arena for your duel. The system will attempt to find an opponent who is close you your ranking in the arena ranking, but if no opponent is found, it will match you with the next available fighter.
The 1v1 arena board can be accessed by pressing F2 and slecting "Arena Rankings." There are gold and title rewards for finishing in the top 10 of arena rankings each season.
1v1 arena is a good way to earn xp and learn combat mechanics.