Player Vs. Player takes place in Cyrodiil

PvP (Player Versus Player) in The Elder Scrolls Online is focused around taking various structures in Cyrodiil.

Players will fight using Trebuchets, Catapults, and all kinds of weaponry to take and hold keeps, structures, and resources around the keep, to get the opportunity to crown themselves as an emperor

You can go to the PvP areas early in the game, even as low as level 10