As outlined in this video from the University of Guelph, you are expected to cite your sources whenever you do the following:
Directly Quote from Other Sources. Any time you directly quote another source and author, you need to include an in-text citation in your work, and a citation in your Works Cited (MLA) or References (APA) page at the end of your paper.
Summarize and Paraphrase Ideas. If you are incorporating an idea from another work or author into your paper -- even if you're not directly quoting them -- you still need to provide an in-text citation, as well as a citation in your Works Cited or References page.
Use Data and Statistics from other researchers and authors.
Source: University of Guelph Library. "Cite Your Sources: When/Why to Cite." Retrieved from https://www.youtube.com/watch?v=ziG9LtIjRUU (CC-BY-SA)
General Knowledge. Commonly known dates, people, events, ideas, etc., are not items you need to cite in your research. Some examples of common knowledge, in the U.S.:
Knowing what counts as "General Knowledge" can be difficult. For example, as a Franklin Pierce student, you know the university is located in Rindge, New Hampshire, but would this count as general knowledge in the wider world? If you're ever confused about what counts as "general knowledge," ask your professor or a librarian.
Your Own Ideas. You don't need to cite any original ideas of your own. That's the purpose of the assignment, after all! However, if you are borrowing ideas from another paper or project you have completed in the past, then you will want to cite this information.