To go a little further... at the top right when you have the 'city' screen view p[en, there is a little tab called citizen allocation focus. If you click that, you can see which tiles the 4 'population' you have are working. There is a green icon in the circle next to the hex that shows that tile is being worked.
You can move those icons around here and if you look at the upper left where your gold/production/culture etc. numbers are, you can see them change. Same with whatever your producing, you can see the number of turns change as you move the citizens to different tiles.
Want to build something faster, move a population or two onto a mined hill... need gold faster, keep them on the gold luxuries and trading posts... growth? food of course.