Paraphrasing by itself does not constitute plagiarism, it is an accepted practice in both scholarly and non-scholarly types of writing. What makes it constitute plagiarism is giving credit to the author who originated the idea while using your own rewording to reword their idea and pretending it is your own. The rule here is fairly straight forward; it's not the words that you borrow from someone else that will require a citation; it will be the ideas.

So even if you completely rephrase an entire sentence in a manner that sounds like you have created the sentence yourself; if the thought, argument or conclusion came from an author, you must still give citation to the original author. There is an additional sneaky way to commit plagiarism known as "patchwriting," where you change a few words from the original and as such, you are referring back to the source as if you have paraphrased the original text. In this situation, you have borrowed the structure as well as the ideas directly from their source. Thus, to avoid all instances of plagiarism, the best policy is to read the original source material and put that aside and write down the main points/reminders from memory and to submit your completed written report, along with a citation to the original source.