You cite your sources to give credit to those people whose ideas/words you are using in your paper and to distinguish their ideas/words from your own ideas and words, to make your argument stronger, and to allow your readers to verify your claims and to get more information from the source materials.
Modern Language Association. Connect to Princeton University's Online Writing Lab for an easy-to-use online guide to Using the MLA format. A paper copy of this style manual is kept at the Woodruff Reference desk:
Gibaldi, Joseph. MLA handbook for writers of research papers. 6th edition. New York: Modern Language Association of America, 2003.
Ref-Desk LB2369 .G53 2003
Chicago Manual of Style
Ref Desk Z253 .U69 2003