This really belongs in the Newbie thread in "General Discussions", but I'll try to answer anyway. Some of what you are asking can be found here.
City Data
The other fundamental thing is that each Citizen (population point) can work 1 square. That square must be within the city's culture radius. (The colored coding on the screen).
Also a city can only work the 18 squares arount it in this pattern. All cities work the City square in the middle.
[EDIT] That should be the 20 squares around, not 18.
0XXX0
XXXXX
XXCXX
XXXXX
0XXX0
C=city square
X= Workable square for city
0= Unworkable sqare for city
So if your city has population 4, you will be working 4 squares (unless they are specialists). This means 5 squares are worked, the 4 by the population + the central city square. Each square contributes an amount of food/production/commerce each turn. These are added to the Food and prodcution boxes.
So if too many of the squares overlap, you are going to have growth limitations.
There are 2 boxes in your city display. 1 for Food and 1 for production.
When full these boxes automatically empty and produce something.
Food filling up causes the population to grow.
Production means that a unit or improvement is produced.
