Market Section: How Does It Work?
Open Market menu from the left side panel on the screen.
It is pretty simple as it is all about Supply (Sell Orders) and Demand (Buy Orders). You do not need to know how much units you produce of something, you just need to know if the production of a building is profitable. So check profitability of the appropriate building and what resources are used and what it costs.
So in that Market menu check the Market price for a good of your interest. If market price is listed with a copper icon it means it is under average market price, if it is silver icon it is within average market price range, if it is golden it is above regular market price.
So if you are producing something, the ideal solution would be to have very cheap resource costs and then the building produces something that can be sold very expensive. This way owners of the building will be very happy.
Problem is that everything depends on each other. What you produce is most likely also a resource for something else. So you have to constantly check and fix your economy whenever you change something. Also other countries can influence your market by importing/exporting from/to it on their own, so prices can change and therefore profitabilty of a building can turn into a loss.
If you want to manipulate market prices you can either import/export goods or upgrade/downgrade buildings (higher/lower resource cost and more/less production).
Market prices also tell you what your pops need. If prices too high, demand can most likely not be fulfilled, see Buy Orders vs. Sell Orders. But concentrate on the basics like food first before you take care of luxuries.
So basically all you need to do is constantly fixing the market prices.