You start out by picking a nation/culture (American, French, Egyptian, etc.) and a leader (a famous figure in history) and you begin building a civilization through researching technology (farming, metal working, the wheel, space programs), building and growing cities, and building culture type stuff (religion, governments, etc), building armies, and turn by turn you expand as time goes on through the different periods of human history.
There are different ways to win, either by conquering your enemies in battle, overtaking their cultures, technology races, etc.
Wonderful game. It's a perfect ground floor into the strategy genre. The problem is, it's probably the best strategy game out there so everything may be downhill from there.