Until you have a construction company in your country you are using foreign resources and labor and must pay for them.

Gameplay wise, there is a button that looks like a crane at the bottom right and one that looks like money, when constructing a building. The crane is for planing construction so your construction companies start constructing them.

Inside the construction company you must select where they get the resources like steel and concrete, usually you want some nearby warehouses, if you make the resources yourself make sure to fill the warehouse with them, otherwise buy them from abroad.

People, if they live close to the construction site will go to work there, if its far away you need to buy a bus in the construction site to move the people.

Bear in mind the game tells you how much working days it is needed to build any building and how many resources you need, its only if you are buying the building when money matters and the game gives you an amount based on how much the labour and resources cost.