PvP is Player vs. Player battling. The Battle Arena is a place where many people come to test their skills with other adventurers in combat, but be very careful while wondering around. If you give someone the opportunity to attack you they will take it, even weaker players are challenged by the strongest adventurers in Denzar.
In your account options you have to choice of turning Peace Mode on or off. If you turn this off you open yourself to be attacked by any other player stronger than you. Beware for some lurk in the background just to attack and gain from other players.
When attacked, the one attacking you can gain experience from you and crowne, keep all crowne in the bank and not in your pocket if you choose to have this off.
If you keep Peace Mode on then you will be protected from other players attacking you. The choice is yours.