Based on what the trailer reveals, it looks like the game unfolds in two basic phases. Daytime hours will be used to build up your fortress in the stylized, seemingly post-apocalyptic landscape, using whatever debris and other resources that are available. The nighttime hours are then spent holing inside the fortress while all manner of slavering nasties — including zombies, from the look of things — try to break in from the outside.
There’s no gameplay in the trailer, so bear in mind that there’s probably a bit more going on than that. We don’t even know what platform(s) the game will be released on, or even what kind of release model it will be using (ie disc vs. digital). Now that the formal announcement has been made, however, you can probably expect to hear more about how the game will work soon enough.