Very Easy. There is almost no chance of you losing this level.
To win this scenario you have to create 4 militia.
As soon as you begin the game you will notice that you have plenty of resources. Send one of your villagers to build a house. With the other three villagers build a barracks at the same time.
As soon as the barracks are finished click on it. Click on the train Militia button four times. Now watch as the militias are created.
Once four militias are created the game ends with you being the victor.