Look on the front page. Look at each heading. You will see one called Front Lines. Click on it. Near the top left you'll see a blue button called 'new thread'. Click on that.

Title: Enter both battlers names
Message: State the rules of the battle.
Click: Yes, I want to slaughter this wannabe emcee
Enter: the exact member's name you are challenging in the Option 1 below
Click: Submit New Poll