The mode has teams of four fighting in Stalingrad against the zombies of Oberfuhrer Wolfram von List, who is reviving fallen soldiers from the Eastern front. He gained this power by bonding with an entity known as Kortifex The Deathless. I don’t know what they bonded over - perhaps they both support Huddersfield Town. Players get to use new magic powers, too, by bonding with four other magical entities who oppose Kortifex. The others are Saraxis the Shadow, Norticus the Conqueror, Inviktor the Destroyer, and Bellekar the Warlock. I’m guessing stealth guy, ice guy, fire guy, etc. There are also upgrades you can get at altars around the map, which randomise after each objective. A blog post with more details on the Call Of Duty site offers the “Ammo Gremlin” upgrade as an example, which reloads non-equipped weapons over time, and “Brain Rot”, which turns zombies to your side. Zombies mode has cross-play with consoles and shares player progression with the main game’s multiplayer and Call Of Duty: Warzone. You can also find more details by watching this longer developer walkthrough: