/ Key: Add Resources - click on a city and then press this option key.
Exit from the city and you will see you have more resources.
This option shuts itself off after about 3 seconds. Please
note that you have to discover and have some of the resources
already to increase the number of them using this option.
Can't get much clearer than that!
Right the food does work. Note this option does not effect the amount of food coming into your city.
In the link above you will see that the arrow is pointing on the word Citizens. There is a box just next to it on the right. Now that box shows how much the City has in food! All option 0 dose is max that out. It dose not change the amount of food coming into the city. So you still have to manage that or there will be starvation as there is not enough food coming into the city.