The arena is the place where you can engage in PVP combat.

 It will be available when reaching castle level 4. 

 You must form your heroes to challenge other players in the arena. 

 You will receive points for each win. However, if you lose, the points will reduce. 

 You can use the currency in exchange for items in the store. Every day, you will get the arena currency. 
At the end of the season, you will also get rewards based on your rank.