MaliceX said:
1) My big cities always get unhappy and sick. I build temples, granarys and lots of stuff to increase happiness and cleanliness, but all that is ALWAYS not enough to outweigh the "Its to Crowded" thing. I figured if I built more cities it would disperse my pop, but it doesnt.
"It's too crowded" is just about population size; the bigger the city, the bigger this value. Likewise, each population point adds unhealthiness.
Unhappiness can be dealt with a number of ways. Each Religion in a city allows you to build a Temple for +1 happiness; there's also your state religion or (later in the game) the Free Religion civic for religion based happiness. Luxury resources will add

too, if they have the appropriate 'improvement' built on them (mines for gold, camps for ivory, etc) *and* a route (road, railroad, and/or river) linking them into your cities.
Once you research Drama, you can also adjust the Culture slider

to add happiness (the exact amount it adds per city is shown on the city screen in the top-left, by the culture bar).
Some of the civics can help with unhappiness too; Hereditary Rule is a good general purpose one (+1

for every military unit in a city), and there are others for more specific issues. And of course there's always Slavery to cut down on your population... at the cost of more, albeit temporary, unhappiness.
Unhealthiness can be solved by Health resources (eg. Cows, Rice), again with the appropriate improvement and a route. There are a few buildings that increase health (Aqueducts, Granaries, etc), and a few that increase unhealthiness (Forges, Factories, etc). Also, having Forests close to your city (in the city radius seen on the city screen) helps a little.
However, whilst an unhappy citizen produced by excess unhappiness does nothing for you except eat 2 of your food, unhealthiness will only consume one extra food per excess

.
Extra cities won't help disperse your population as city growth rates are independent of each other.
MaliceX said:
2) What the heck is my commerce/coin used for. Food gives me growth and happiness, production makes me build faster.
3) what is the research slider used for.
Commerce

is what you obtain from cities working tiles (primarily, cottages and their larger versions). Commerce gets split three ways, depending on the slider settings in the top right.
Research

allows you to discover technologies. The more you spend, the faster you'll get to the high-tech stuff... as long as you have the income to cover it. If you're just starting out in the game, a good rule of thumb is to set this at the highest possible percentage where you're still on a positive (or small negative) income. It's not the most efficient way, necessarily, but it'll get you through the game.
Culture

, as mentioned above, can make your citizens happier. It will also increase a city's Culture rating, which is useful if you're going for a Cultural victory, or if your neighbours' borders are getting a little too close.
Gold

is only explicitly shown in the city screens. Everything left over after research and culture goes into your treasury, to be spent later. You can use gold for upgrading units, for buying production (under the Universal Suffrage civic only), or in diplomacy with the AI leaders (with the Currency technology).