Easy enough, Tito..
In the game screen under "Multiplayer", choose "Create a Game".
If you want a one-on-one match, choose "Match Play".
From the next screen, you can select the rank/tier level, of the players you wish to play against, and set the other game parameters.. then choose "Create Game".
In the next screen under "Add a Player", you can choose "Best Match", and hopefully will find a player close to your skill level...
Also take a look in the forums under FAQ- "MATCH PLAY", you will find all the details..
Hope that helps~~ GedE