Home is a society where all physical needs are met by Automatics that operate beyond human control, giving the gift of civilization... but only for a lucky few.
The ordered, regulated life of Home centred around the games, a life and death event that Susa trained for her whole life. Failure to win means exile, tantamount to a death sentence.
Losers are exiled into a world where technology and civilization have long since failed.
Susa has failed to win a place. Exiled, she crosses the threshold into a whole new world she didn't even know existed.