Some online guides for MLA style:
Purdue Online Writing Lab Guide—Detailed overview of all aspects of writing and citing in MLA style
Concordia University MLA Guide—Straightforward examples of how to cite different types of sources
The 2009 hardcopy MLA Handbook for Writers of Research Papers details citing sources and writing in MLA style and is available in the library:
For other styles see the Tomlinson Library LibGuide help page on citing sources.