To paraphrase is to state in your own words facts or ideas acquired from another source. To quote is to indicate when you are using someone else’s language through specific typographical conventions (e.g., quotation marks or indented block text).
We're going to discuss paraphrasing and quotation to avoid plagiarism. Let's start with an original text from a fictitious book:
Bede’s intent in writing his Ecclesiastical History was not simply recitation or rehearsal of dates and events in early medieval English Christian history; it was to reveal the development of England as a Christian people. The conversion of the Anglo-Saxons was the catalyst for the transformation of disparate pagan tribes into the ecclesia, the gathered people of God, formed and united by a Christian faith.
— Reginald Smith, Christianity in Early Medieval England (Oxford, 1899), p. 15.
Inadequate paraphrase only changes a few words, and shouldn't really be called paraphrase. Consider, for example:
Bede’s purpose in writing the Ecclesiastical History was not to recite or repeat dates and events in early medieval English Christian history. He intended to reveal the development of England as a Christian people. He saw the conversion of the Anglo-Saxons as the catalyst for the transformation of various heathen tribes into the people of God, gathered, formed, and united by the Christian faith.
Very little has been changed. It's still largely the words from the original text (marked with yellow highlighting) and this constitutes plagiarism. Source citation is addressed separately, but in brief, adding a footnote to this text doesn't change the act of plagiarism, as you've still presented someone's words as your own. A more thorough rewrite (i.e., a true paraphrase) follows:
Bede’s authorship of the Ecclesiastical History was guided by a specific intention beyond merely recording a timeline of events in the history of Christianity in early medieval England. He was concerned with narrating England’s growth as Christian nation and showcasing its conversion from an island of non-Christian tribes into a unified Christian people.
You can quote the original text judiciously within your paraphrase, if you want to highlight a specific phrase or word choice:
Bede’s authorship of the Ecclesiastical History was guided by a specific intention beyond merely recording a timeline of events in the history of Christianity in early medieval England. He was concerned with narrating England’s growth as Christian nation and showcasing its conversion from an island of non-Christian tribes “into the ecclesia, the gathered people of God.”