I watched S01E01 angel of death - infodump at me so I understand it - Divisions by zero

Basically title. I watched Angel of Death S01E01. I’ve played (a? Some? Idk.) warhammer video games and it/they were fun (some of that stuff is sneaky and you don’t know what your playing until bam it’s warhammer, what??) and I assume entirely unrelated. But this I don’t really get so tell me all the lore I need to know to understand what I just watched so I can watch the rest of it and enjoy it. No llm, only passion infodumps, please.