When you quote or paraphrase from a source (book, article, or webpage) in your paper, you need to insert a parenthetical citation. This citation typically consists of the author's name, year of publication, and page number in parentheses at the end of the sentence.
Using Parenthetical Citations is important when you want to cite from other sources. You use it when you want to "refer to, summarize, paraphrase, or quote from another source".