What is the purpose of parenthetical or internal citation?

In MLA style, in-text citations, called parenthetical citations, are used to document any external sources used within a document (unless the material cited is considered general knowledge). The parenthetical citations are used to direct readers to the full bibliographic citations listed in the Works Cited, located at the end of the document. In most cases, the parenthetical citations include the author's last name and the specific page number for the information cited.