There are two types for resources, consumables and permanent resources. consumables resources are used for one time payment for a building or research. permanent are payed permanet and block a specific amount.
Consumable Resources:
- Stone
- Wood
- Gold
Permanent Resources:
- People
Stone and Wood can be produced in a Stone Mine and the Lumberjack Hut Gold is produced by People that are not assigned to military Since People is a permanent resources you increase the maximum for people by building living places and upgrading the houses.
People are used to work inside a building so every building which is not a Living House blocks an amount of people to work there. Those people will produce Gold. Creating Military Units also Blocks People but those units do not produce gold. People which are not assigend to Military or Buildings are not producing Gold as well.
The Idea is that you have to manage your City, the amount of Building to place is limited. So you have to decide you build a city more with units or more for Resources.