MLA style is the style commonly used for the study of modern languages, including Spanish. Unfortunately, the MLA Handbook is not available in electronic form but there are several online sources for MLA citation and the library subscribes to Refworks which will format your citations to MLA style.
Two excellent online sources for MLA style are Research and Documentation Online and The Everyday Writer. An internet search will find other cheat sheets, but when in doubt, check against the MLA Handbook or ask a Librarian.
The MLA Handbook for Writers of Research Papers, 7th ed is also available in print form at the King Library Reference Desk.
Typically, MLA style uses in-text parenthetical citations with a list of works cited. If your instructor asks you to use footnotes or endnotes, see Appendix B of the MLA Handbook.