Production buildings are the ones you can use to produce the useful resources. In order to start production, you need to buy the appropriate building in the market and place it on the available territory.
Tap on a building and drag an item or product to a free slot. The production of each product can be accelerated for gems. Also, with the help of gems, you can open additional slots.
As soon as the products or items are ready, you can see them above the building and collect them.
If you do not have enough resources for production, tap on the magnifying glass and follow the yellow arrow. It will point you to the place where you can find the needed resource.