Hello!! I'm new here and a complete newbie to civ4!! i see alot of potential in this game and really want to get into it but there are some areas which i am getting stuck in. I have read several guides and read through sulla's walk-through guide but i am still confuzzled!! i made this post in hope someone would be kind enough to explain a couple of things, so i apologize in advance if its a little lengthy and too many questions , but it's the only way I think I can understand enough to start understanding why I'm doing things, rather than guessing 
I'm slowly starting to understand the city management screen but I'm finding some parts confusing. They are the food bar and production bar and the white circles (which I think means which tiles are being worked on).
Firstly, I don't understand what it means by 15 -13
for instance?? I can see that I'm getting 15
from the tiles that are circled but what does -13 mean?? and what does it mean when i have an increased portion on the actual bar (the section with lesser opacity).
It's pretty much the same deal for the production bar aswell. I notice that it is used to build things but am not quite sure whether it means I have 4 physical
to spend as such or I am earning 4 a turn, Im guessing its the latter, which would mean that every turn I'm producing 4
. So, if I'm building say; something that is 100, @ 4
a turn it would take 25 turns?? ..i think i may of just answered my own question there lol but am not sure. again what would 4 -2
mean with the production bar?? and yet again what does it mean when I get an extra portion on the bar (in the lesser opacity).
Next is the white circles, im guessing these are which tiles the city citizens are working on???? how come i can choose more circles in some cities?? what do i need to be able to work on more individual tiles and what effect does this have?? also if a tile isnt circled but i have built say a farm or mine on it, am i getting the food/production from that tile??
Lastly (and the long bit, hehe) from reading these guides I see that I need to specialize my cities. One for production, one for commerce and one for Great people/specialists. I understand this is the best way to go but should every city have at least some of all 3?? Do i need lots of cottage tiles in each city to accomodate more citizens?? The more food I am harvesting from tiles the more people I have in a city? Or do they need cottages to live in (lol I think that is a silly question!)
The great people city...this should harvest lots of food I have read, and with that I can 'buy' specialists which generate great people points right?? Should I build all my wonders in this city aswell??? Or would it be better in the production city where it would build faster??
well, thanks for reading this far if you did and a big thanks in advance to any help given. !

I'm slowly starting to understand the city management screen but I'm finding some parts confusing. They are the food bar and production bar and the white circles (which I think means which tiles are being worked on).
Firstly, I don't understand what it means by 15 -13


It's pretty much the same deal for the production bar aswell. I notice that it is used to build things but am not quite sure whether it means I have 4 physical




Next is the white circles, im guessing these are which tiles the city citizens are working on???? how come i can choose more circles in some cities?? what do i need to be able to work on more individual tiles and what effect does this have?? also if a tile isnt circled but i have built say a farm or mine on it, am i getting the food/production from that tile??
Lastly (and the long bit, hehe) from reading these guides I see that I need to specialize my cities. One for production, one for commerce and one for Great people/specialists. I understand this is the best way to go but should every city have at least some of all 3?? Do i need lots of cottage tiles in each city to accomodate more citizens?? The more food I am harvesting from tiles the more people I have in a city? Or do they need cottages to live in (lol I think that is a silly question!)
The great people city...this should harvest lots of food I have read, and with that I can 'buy' specialists which generate great people points right?? Should I build all my wonders in this city aswell??? Or would it be better in the production city where it would build faster??
well, thanks for reading this far if you did and a big thanks in advance to any help given. !