MLA is a style based on the MLA Handbook, published by the Modern Languages Association. It is used in many English classes, as well as other disciplines in the arts and sciences.
MLA uses parenthetical citations that include the authors last name and a page number, after the sentence in which you've used the source as evidence. The in-text citation directs the reader to your works cited page where they can find the full information on the source you are citing. This lets the reader follow up for more information or check on what you have used as evidence.
An MLA style paper concludes with a works cited page that lists a full entry for all of the in-text citations.