The world is frozen over. You live with others in an underground compound. All the others are players. Theres lots of little things that you can do to help the colony survive and thrive. Growing and tending plants in the greenhouse, cooking food, repairing machines, exercising, decorating, etc… If everyone contributes a little bit and works together, the colony will thrive.
You can go out into the frozen wasteland, but you need plenty of supplies to survive. When you go out there, there is cool stuff to find and bring back to the compound. And, you can find other compounds with other groupings of players. Its not too common, but when you find another compound you can start trading with those players. You can even migrate over there if you want.
The initial compound you are put into is random, but each one only holds a max number.