Plagiarism is using another person's words without giving that person credit. Always give credit to your source of information; this means explaining where you found your information. You cannot copy a sentence word for word, unless you put it in quotation marks and give credit to the source. If you don't want to use an exact quote, then you must paraphrase or put things in your own words. If you copy a whole paragraph in order and just change some of the words in each sentence, you are still plagiarizing.