In Mad Max: Fury Road we learn bits and pieces about her backstory – including that she was kidnapped at a young age along with her mother and brought to The Citadel, ruled by the fascistic water-hogging Immortan Joe, and presumably the new film is going to serve to fill in gaps in the history of the fan-favorite character.
The reason why Charlize Theron isn’t playing Furiosa in the spin-off is because the movie is going to be structured as an origin story instead of a sequel.
Unfortunately, because there are no details in the trade report or existing source material, it can’t be said at this stage what to expect from the characters played by Yahya Abdul Mateen II and Chris Hemsworth.