The World has Collapsed
You have the Hideout, you can craft weapons, ammo, and other consumables here. You will also be able to build structures inside the Hideout (similar to Fallout 4's settlement building). From the Hideout, you start missions. Missions belong to a story arch and can influence each other, depending on the order in which you do them.
Projekt Z is a first-person coop survival shooter set in a WW2 Zombie scenario on a secret German island. The game focuses on the threat of "Projekt Z", a clandestine program run by the Nazis to turn Zombies, which have been discovered on the island earlier, into weapons to help turn the tide of the war in Nazi Germany's favor.