Cite your sources to acknowledge others' ideas, work, conclusions, and words. Use a standard format and apply it consistently. Your readers will be able to track back to the facts, theories and inspiration on which you have built your work.
Purdue OWL is the go-to guide to detailed help for various citation styles, including MLA, which you'll use for this class. (MLA 8th edition released in April 2016.)
Plagiarism, that is, misrepresenting someone else's work as your own, is a serious violation of Cornell's Code of Academic Integrity.