Once you receive this quest, a new location appears on the World Map, marked as Refugees. Travel to the location ,and fight the darkspawn (see here for details on the fight). Once the fight is over (regardless of how many, if any, refugees you saved) return to a Chantry representative for a reward.
Note: The reward is not affected by the number of refugees that survives the fight
Note: I received this Quest from the Chanter's Board at Denerim before I had visited Redcliffe and had to return to Denerim to be rewarded.