When you are using a war table in Haven, there are several missions open to you that have a time limit. Send one of the three troops that it says to that mission. After a certain amount of time, a message will pop up as you do whatever to return to the war table Go to the mission where you sent the person and it will give you a reward for doing said mission. You only need one mission but there are some really nice rewards tied to some of them so do as many as you can as you play.