When you compare and contrast two pieces of literature, you are showing the ways in which the works are the same and the ways in which they are different. Before you start writing your assignment, you need to review both works to determine what similarities and differences you are going to explain in your paper.
Similarities between these two stories could start with the fact that in both, the main character is a child whose family is forcibly moved from its home to a restricted and enclosed area due to an official government policy of discrimination against the family's ethnic group. In both stories, family members are separated, many hardships are endured, persons struggle to understand why this is happening to them and how to maintain their identity in the face of the dehumanizing conditions in which they are being held. In both cases, the narrator of the story survives and becomes a spokesperson for all who were in the camps in later years.
Differences between the two stories are many. The specific ethnic and religious identities of the exiled persons are different - Japanese in one story, Jewish in the other. Many of the Jews are exterminated by the Nazis, while many of the Japanese are allowed to return to living in the general society of the United States after the end of the war. The types of activities undertaken by the persons in the different camps are very different, reflecting the differing attitudes toward the camps' residents by the governments of the United States and of Germany.
Once you have your lists of similarities and differences determined, you can begin to develop your paper.