The Loudoun Campus Writing Center has several handbooks you can use, and you should own one if you've taken English 111. You must be painstaking about your accuracy in quoting from outside sources. In all these cases, the original author must be acknowledged, and your writing should make it absolutely clear if you're quoting, paraphrasing, or summarizing. BUT you also plagiarize when you simply borrow an idea or a train of thought without citing the author.
Plagiarism is a very serious offense.
Make sure some form of this statement appears in both your introductory and concluding paragraphs.