Hm, I can't personally accurately explain it. It really depends on how far you want to take it, you can micromanage everything. You start with a city and build up an empire. Each tile consists of work points, money points, and food points. You build city structures on tiles to boost whatever in your city. The number of tiles you can have affect the city relates to your population. You need food for the population, workshops to keep up with the city's advancement demands, as well as the totality of your empire, and money for everything, so you can't really have one without the others too much. Inside your city are numerous buildings that you can build up to affect culture, tech, happiness, and cleanliness, as well as unit production buildings, air fields, defenses, wonders.
You also build roads between your own cities and other civilizations for faster unit movement. As well as preserve forests for happiness and cleanliness.
Diplomacy plays a big part of the game. Trading and selling techs, giving gifts to please the ai and cease fire when they are pwning you.
Battles are basically roll the dice. You see the probability of winning. Attackers seem to have a much better advantage by getting the choice of what units attack first, maximizing flanking and cannon damage spread, though defending gets defense bonus of terrain and any entrenchments.
There's also spying and sabotage, which I don't really partake in too much.
Nukes are always funny, but too much of them degrades the world and sends in into global warming.
By game default, you can win in like 7 different ways, culture, economical, technological, conquest, some other things.
I think there's really too much to explain for a little post.
None.