The idea is to add a second phase to the game, that is perpetual; it doesn't really end. The goal is simply to support as large a population as possible, and keep them as happy as you can.
There are four parts to this:
- You need to provide space for your colonists to live. It's as simple as dragging out zones in which they can build their cities, where they will construct and maintain the buildings they want on their own.
- Your electrical grid must support their needs, in addition to your own.
- You need to meet an ever-increasing demand for supplies. This consists of farming machinery, construction machinery, construction materials, fuel, electricity, household and business supplies, and optionally, nonessential items (primarily electronics of various types). You don't have to worry about food; they will make and store food on their own. But, starvation is a real thing. If they can't maintain their farms, things will go south in a hurry.
- You also need to defend these cities from the local wildlife. Basically the same thing as defending your factory. The cities will produce pollution on their own. You don't have much control over how much they're producing.