Speak with Squire Danny to summon your opponent. Once you have defeated the Argent Champion, return to Lana Stouthammer at the Argent Tournament Grounds.
If you lose your lance, you can get another from any of the Lance Racks near the stables or in the Silver Covenant Pavilion.
You are nearly ready to compete on behalf of Ironforge in the grand melee. To prove yourself worthy to enter the lists on behalf of our city, you must defeat a champion of the Argent Crusade.
Go to the stables outside the pavilion, equip your lance, and mount up. Speak to Squire Danny at the Argent Valiants' Ring on the western edge of the grounds. The squire will call out your opponent when you're ready.
After the battle is concluded, we will speak of the outcome.