It is unethical and illegal to use someone else's ideas or words without giving them credit. You should cite (to quote or give credit) the source. Use this guide to help you create citations for your academic work.
First determine if your sources is a book, article, website, speech, newspaper article, blog, or something else? Usually, your professor will ask you to use a certain style: APA, MLA, Chicago, Turabian, IEEE, etc.
Ask a librarian if you have questions. We are here to help you.