The Suburb is the close surroundings of your City, the place where you probably start your first babysteps in the big bad world! You can train your low level Hero on monsters between level 1 and level 20 or Improve your Farms and Mines.
Traveling in Suburb costs no food, you can freely move your Hero around untill you want to head back to your City.
There are four types of resources you can harvest in the Suburb, Metal, Lumber, Food and Stone. These resources are the building stones for everything you will make in your city. So this place is the engine of your power, without these resources your movement and improvement in the game will be very limited. For more detailed information on the various Suburb buildings click the following links.