How do you get arena rating on wow

Arena rating is obtained by participating in 3v3 or 5v5 arena battles at level 80. You will need to be part of a team, and you will receive an initial rating (1000 or so I believe) upon which your results are based.

If you win from a higher-rated team, you gain a lot of rating, if you win from a lower-rated team you gain less arena rating. Likewise, losing from a lower-rated team is more damaging than losing from a higher-rated team.

This rating also applies to your team as a whole, working from the averages gained and lost. You will need to have a personal and a team rating above a certain amount to be able to purchase the most powerful PvP items.