Whenever you quote, paraphrase, or summarize the findings or ideas that aren't your own, you need to attribute that information to the original author(s) it came from. Failure to do so is considered plagiarism.
Attributing information to another author is done by what is called citing or referencing that author. Depending on the style your professor asks you to use, this may be accomplished by using either in-text citations or footnotes. You will also be expected to include a list of full citations that describe each work and enable your reader to locate the item. This list may be referred to as References, Works Cited, or a Bibliography depending on the citation style you use.