The arena is a system in which you are allowed to battle other players playing hero world. You can challenge heroes by clicking on the red tab labeled challenged, and it will send a request to that hero, and if that hero accepts then the battle screen will automatically load and you will be able to chat and fight with that opponent. There is also a find a battle tab, which sends out mass requests to all heroes in the arena, and usually loads up a battle faster then just challenging heroes.
The arena has ranks according to how you perform against other players, and these ranks give access to buying powerful items.
The arena ranks are divided into two groups: