What is the main problem or theme in Out of the Dust?There are so many problems in the story that I can't figure out the main problem.

You are absolutely right; Out of the Dust does, indeed, have very many problems.  The main problem, though, seems to be survival in very harsh situations.   Billie Jo Kelby, the fourteen/fifteen year old girl from whose first person point of view the story is told, in journal form, survives an unbelievably harsh life during the Depression in the Oklahoma Dust Bowl.  Follow the link below for more information about Out of the Dust.