Explain existentialism and quote text from "hope, despair, and memory

Existentialism is a philosophy that gives value on individualism. It focuses on man's interest, endeavors, and achievements.

An example of a quote from the novel of Elie Wiesel related to existentialism is, 

“And now the boy is turning to me. “Tell me,” he asks, “what have you done with my future, what have you done with your life?” And I tell him that I have tried. That I have tried to keep memory alive, that I have tried to fight those who would forget. Because if we forget, we are guilty, we are accomplices.

The excerpt was clear about the concern of the boy in his future while the answer was also about fighting for life, survival, and saving the memory of the past to tell history.