MLA will affect your paper in three places:
The general format of the paper. This includes margins, font, page numbers, line spacing, titles, headings, etc.
The bibliography. The bibliography is the cumulative list of all sources used in your research. In MLA, this is called the Works Cited list; in APA it's called References, and in Chicago it's called Reference List.
In-text citation. Citing sources within the body of your paper let's your reader know where you are incorporating someone else's words/research/ideas, and where those words/research/ideas come from.
For full details on how to format your paper, cite your sources, and incorporate in-text citation in MLA style, please visit Ready, Set, Cite.