MLA (Modern Language Association) uses the author-page format for in-text citations. After you have quoted or paraphrased the words of an author, put in parenthesis their surname and the number of the page:
According to Smith (134) the planets revolve around the sun
"Planets of our solar system orbit around the sun" (Smith 134)
Surname, First Name. Title of Book in Italics. Place of Publication, Publisher, Publication Year.
Teitelbaum, Joshua. Political Liberalization in the Persian Gulf. New York, Columbia University Press, 2009.
Surname, First Name. "Title of Article." Title of Periodical in Italics, vol. number, issue no., Day Month abbreviated Year, pages.
Kang, Jaeho. “The Ur -History of Media Space: Walter Benjamin and the Information Industry in Nineteenth-Century Paris.” International Journal of Politics, Culture, and Society IJPS, vol. 22, no. 2, 3 Jun. 2009, pp. 231–48.
Author (if available). "Title of webpage." Title of Website in Italics, Latest date, Permalink. Accessed date
Kephart, Beth. "The Four Times I Became a Writer." Literary Hub, 10 Sept. 2018, https://lithub.com/the-four-times-i-became-a-teacher/. Accessed 11 Sept. 2018.
A primary source can take various forms, it could be an image, a video or manuscript. For each form you need to follow different rules in order to cite it. Check out Purdue OWL MLA Guide to find out more.