You asked multiple questions but are only allowed one per posting, unfortunately; so I had to edit your post.
In chapter three of Elie Wiesel's Night, the Jews who have been herded into cattle cars finally arrive at Birkenau, the reception center for Auschwitz, the notorious death camp. Immediately the separating and sorting process begins for Elie and the others.
Another prisoner warns Elie and his father not to declare their real ages; Elie should claim to be older (eighteen instead of fourteen) and his father should claim to be younger (forty instead of fifty). This might keep them alive, as those are the ages at which people are still useful to the Germans as workers.
SS officers with guns separate the men and women, and Elie and his father are separated from Elie's mother and sister.
I didn't know that this was the moment in time and
the place where I was leaving my mother and Tzipora forever. I kept walking, my father holding my hand.
Elie must pass by the now-infamous Doctor Mengele and claims he is a farmer rather than a student, thinking this will make him seem more useful to his captors. He manages to stay alive, and he and the other lucky ones then have to suffer the indignities of being stripped, showered with disinfectant, and shaved (to prevent lice). Some clothes are carelessly thrown at them and their arms are tattooed a few days later.
Presumably Elie's experience is similar to what is happening to the female Jews, but of course Elie has no way of knowing that at the time.