Here you can find the rules for challenging other players in Pokémon battles.
There are a few thing to consider when challenging other players, what level they are, what type/types of Pokémon they have in their party.
Choose your opponent carefully, because once you've entered a challenge you cannot leave or flee.
To issue a challenge to another trainer you must be a registered Pokemon Trainer, i.e have a Character Page and a registered Starter Pokemon. If so, you enter the chat and look for a Referee and an Opponent. If both are present you can issue a challenge, if the challenge is accepted give the referee a few minutes to set up and he/she will let both combatants know when the battle starts.
The challenger gets to choose the arena for the battle giving them an edge when the battle starts, as some Pokemon are better in certain arenas.
The referee will take your Stats into account when the battle rages on, and as sufficient amount has been done to a Pokémon and it's HP stat is down to zero that Pokémon is knocked out.
The Winner gets awarded PokePoints and PokeCoins depending on how intense and well written the battle was, here's a reference for amount of PP and PC the trainers can get depending on their level.
-- WILL BE ADDED SOON --
These are the referees available at this time
Interested in becoming a Referee? Then PM Destruction87 for a chance to guest monitor a battle, and if your referee abilities are satisfactory you might get registered as a official Pokemon Battle Referee.