Every time that you directly quote information, or paraphrase information from a source, or summarize information from a source, you need to provide an in-text citation. The only time that you do not cite information is if the information is considered to be common knowledge. MLA style considers common knowledge to be information which could be found in common reference sources, for example, the name of the 16th President or the birthday of Martin Luther King, Jr.
Rules for In-Text Citation:
When you cite a source, include the author's last name and the page number where you found the information that you are citing. Put this information in parenthesis; no commas are needed. Place this citation at the end of the sentence with the period on the outside of the parenthesis.
If you are citing a source which does not have an author, use the first two or three words of the source's title, ellipses, and the page number.
("Title . . ." #).
("My Cats . . ." 63).
No Page Number?
Web publications often have no page numbers; the MLA Handbook recommends putting the author's name within the text or including it as a parenthetical citation without a page number.