This achievement is pretty easy in understanding what is required for its accomplishment, just simply search for an online player vs player duel match and win the match by beating your opposition in 3 out of 5 rounds.
The only real difficulty to this achievement is that the servers have died down a bit over the last year or so meaning that the majority of people in PvP duels will be relatively good at the game and provide some what of a challenge. However just keep on playing and eventually you’ll win a game and probably become a more skilled player along the way.