Explore the more common style guides listed under the main Citation/Documentation page above: APA, MLA, and the Chicago Manual.
According to Fordham's Academic Honor Code, "plagiarism occurs when individuals attempt to present as their own what has come from another source. Plagiarism takes place whether such theft is accidental or deliberate. It is no defense to claim that one has 'forgotten' to document ideas or material taken from another source . . ."
Become familiar with the writing style guide suggested by your professor. Almost all subject areas have their own style guides. The more common styles are presented under the page "Citation/Documentation;" APA, MLA, and Chicago Manual of Style (CMS).