Desperate Haven is a quest received from the Chanter's Board in Redcliffe Village or Denerim. A group of refugees is fleeing the darkspawn, and the Chantry would like The Warden to assist them, if possible.
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.