What is the first thing that happens when Elie's family arrives in Birkenau?

When the family arrives at Auschwitz, the men and women are separated, and Eliezer sees his mother and sisters vanishing in the distance. He holds onto his father and is determined not to lose him. A fellow prisoner tells Eliezer to say that he is eighteen (though he is really fourteen) and that his father is forty (though he is fifty). The prisoners who have been at Auschwitz for awhile are brutal and cruel to the new arrivals, and one of them tells them about the crematory.