Ever notice your short on Food, Lumber, Stone or Iron? Ever notice when you go to bed and then the next day you have more resources?
This is called Net Production. Where you can see how much resources you have, look to the right and you will see some green numbers. The green numbers mean how much of that resource you get per hour.
To improve that number so you can get more resources by the hour, click on city. Then, click on the square, a farm improves food by the hour. As you build a farm, you see the green numbers go up.
This is how you get more resources!
Sawmills produce Lumber, Quarries improve stone, and Ironmines producte iron.
Now when you go to bed, and wake up the next day, you will have more resources than you have before you made the resource fields.