You make cities, roads, railroads, irrigation, etc. with settlers. You must organize city resources to maximize trade, raw materials, and food. If you city does not have enough food, people starve. Above this is a number signifying population. The higher a city's population the the more resources you have to manage and the more people to use.
People can be farmers, wise men, business men, etc.
The higher a city's population, the faster it is to build things. Other Information Lee Gordon has made a chart linking the advances in the game into a nice diagram. It's available in postscript format . I've also been told there is a version for the Atari ST, but have no idea how you could find a copy. 3 steps to a square next to your first ship.