Cite the sources in the paper and give the refereces otherwise is plagiarism.
For each immigrant group (ie. Mexican, Chinese, Puerto Rican, Arab), know general things about it. Know the trajectory the group took (what their immigration experience was like: why did they come, how did they settle, what obstacles did they encounter, what level of assimilation did they end up having), know if there are any contemporary issues involving the group (ie. Puerto Rico’s question over whether it will become a state), know where the group stands in terms of occupational and educational attainment, know if it has any similarities to other groups (ie. The Chinese and the Italians), and what their various experiences might say about America or the American experience. Obviously, each group has different things that are unique to that group (ie. The various names for the generations of Japanese-Americans), be familiar with those.