Start with this website:https://malignportents.com/
This video released recently explains it pretty well:
Lexicanum also has plenty of content:http://whfb.lexicanum.com
Thanks, thats quite useful
So basically from the old world:
Order is composed of the old Elves, Empire, Dwarfs
Chaos is Archaon and Daemons
Destruction is the old Orcs and Goblins and Ogres
Death is Undead, Vamp Counts
Skaven live in a sort of underworld and Lizardmen dwell in space cities
Each of them then live in a realm of their own and they can fight each other by invading realm gates and nexuses?
That about right?