Construct buildings from the “Infrastructure” tab and complete the Super-quests (Superzilla, Nessie, Genie, etc.) to increase your population limit.
After that, building new houses will attract new citizens to your city.
After you increase the population new buildings will unlock and you will be able to place them in the city.
Example: Here you can see that the coffee shop needs population of 400. Once you have enough population, then it will unlock for you.