The idea would be starting as nobodies, then becoming somebodies, and eventually sacrificing thousands of innocents in an orgy of death and destruction to appease our dark gods. You know, Warhammer stuff...
Thatīs if you want to play "the baddies". If youīd rather play the goodies, thatīs going to be a little harder and probably best left to some good, old-fashioned small-party-on-an-aventure kind of story, which is what Greentide would be about (like Vermintide, the melee action game, but with the obvious enemies instead of Skaven).
Personally, though, Iīm all for Norsca. And all you need to know about them, you can find easily here:
No one should need to read all of this, but whatever information you seek, you can find there. For the most part, though, Norscans are basically barbarians that worship the dark gods, and they consider that the mutations and transformations that many of them suffer are not curses, but blessings from the gods whom they serve by spilling blood and carrying out dark rituals in their name. Thatīs when they are not sailing south to raid the Empire, Bretonnia or Kislev, or go somewhere more exotic.