Upon entering the Arena, you should be transported to a random player's village that is not under protection.
Upon arriving at that village, a 30-second counter will begin to give you some time to decide whether you want to attack that village or not.
(For example, you may decide that player does not offer enough morale or loot to make the attack worthwhile.)
If you choose not to attack that player's village, you can Skip to the next random village or you may end Arena mode and return to your village.
If you enter the Arena while under protection, that protection will be dropped whether you attack anyone or not. You will be reminded of this upon entering the Arena and given the choice to exit the Arena before your protection is dropped.
You are given 1 min and 30 seconds to attack that player's village.
Revenge is another function of the Arena. After being attacked by another player, you have the option to seek revenge on that player or turn that player over to your Brotherhood's Revenge Journal, which would allow anyone in your brotherhood to seek revenge on that player's village. Your Protection is treated in the same manner as above. You will not be able to revenge a player if they are under protection - you will have to wait until their protection drops. Once you choose to attack, the record of that player's attack will disappear from your mailbox or your Brotherhood Journal and you will no longer be able to revenge that previous attack. Also, a player cannot revenge an avenger. However be prepared; upon ending your attack, your village will be accessible in the Arena mode.