So say you get nobled on W11 when you log in it tells you lost your village (or if your on when the attacks hit) Then it gives you the option to restart or to join Casual.
This is to the best of my Knowledge anyways as iv never joined it before but iv read about it.
The world has a restriction on attacks ( i think its 10%?), so if you join and your next to a 100k player or anyone bigger you won't automatically be easy pickings for them, until you grow close to their size