Have you placed a building somewhere, but decided to move it to another spot? Tap on the building and hold for a second, then move the building to the place where you'd like to place it. Make sure the area is clear (no grass, stones, or other obstacles). Tap the green checkmark 
to confirm.
to confirm.
There is also an option to rotate buildings in the game. To do this, tap on a building, hold for 1-2 seconds, in the menu that opens tap the blue button to turn the building and the green button to confirm:
