When you use the words, ideas, or creations of someone else, cite them. To make it easier to keep track of your sources, try a citation tool like Zotero. Not sure how to properly format your citations? Citation styles (MLA, APA, Chicago) give you detailed guidelines. The citation style you use will depend on the discipline, journal, or course for which you are writing.
Zotero will automatically generate bibliographies and format your research papers in any of hundreds of styles including MLA, APA, Chicago, and Turabian. Zotero is easy to learn and has exciting features.