We have a section of the Player Guide specifically on PvP and you can find it here: PvP - Player Guide
The Player vs Player Arena is located in Unicorn way, inside the current dueling arena. Just look for Diego, he's standing next to the entrance. Inside you will find two Guards.
The Guard on the right is for Practice Dueling and all players can participate in this. The Guard on the left is for Ranked Dueling. These are duels that can earn you Arena Tickets and are only available to Subscribers or with Crowns on a Pay-as-You-Go plan.
Ranked matching occurs thru a formula that takes a number of factors into account, including level, win/loss ratio, PvP Rank and available players. When you’re competing in teams, the dynamics of choosing your partners and opponents gets much more intricate, taking into account the level, rank and win/loss ratio of ALL the participants to try to create the most even duel it can, with the players that are available.
Paying Players can see their PvP rankings in their character screen. Just press C when you are not in combat and you will see the PvP panel tab on the right. These rankings should show up on your character sheet, on purchase requirements for some arena gear, and in the Name Tag next to your title. This pvp icon will show up during PvP combat only. When it does show up your Badge will change from the selected badge to the Ranking Name. When you leave combat it should go back to your selected badge.