Trade is an integral part of the city budget. Already after tens of minutes of the game you will be able to sell the surplus and you will have the need to purchase shortages.
1. The city in its buildings produces some goods as Fuel, Electricity, Water Heavy Industry's goods or Office Services. It uses it on its own but usually produces a surplus that can be sold for cash.
2. Sometimes a city can't handle certain fields on its own, for example, in the desert there is no water and you will need to buy it. However, try to supplement deficiencies as much as possible in the city, e.g. if there is no office services build additional plots for offices.
3. Exchange will be made in the form of so-called tokens. Production of tokens should be the main objective of specialization of a town in specific locations on the globe.