Even if your professor doesn't tell you to cite your sources, you still have too. Chances are, if they didn't tell you, they just assumed you know it's required. Any source you get information from whether it is an interview with a person, a pamphlet from a government office, a web page, a journal article, a book, etc. requires a citation. When you use that sources' information, you must give them credit; if you don't you, you are plagiarizing.
(From Merriam Webster Online.)
Explore the links below to learn more about Plagiarism and how to avoid it.