A citation is a referral to an information source. It is usually provided as a combination of title, author, date and location (e.g. URL or DOI). Citing your sources is the best way to avoid plagiarism. Plagiarism can be deliberate - knowingly using someone else's work as your own. It can also be inadvertent. Sometimes plagiarism accusations are simply the result of not following a specific style properly. The specific citation style you are using will dictate the details. See the Build Citations page on this guide for help with a particular style.
Learn 6 steps to successful paraphrasing! If you want to learn to paraphrase well, Paraphrase: Write it in your own words at the Online Writing Lab (OWL) from Purdue is a great place to go.