When your character is engaged in a conflict with another character then the result of the actions are determined by an opposed roll. The rules are the same as for Challenge levels, however the challenge level is determined based on the character/characters in the conflict.
This is used in situations that require specific Character Traits to resolve. Examples include sneeking past guards, debating a political position, or outmanuvering an enemy comander.
In a situation where two characters are involved in a melee fight, the rules for a Duel are used