Purdue University's OWL (Online Writing Lab) site has a lot of information about writing about specific subjects or for specific purposes, and about the various kinds of writing styles.
Under Research and Citation are guides to:
The APA and MLA pages both have links to "Formatting and Style Guide," which is where you will find specific examples of citing articles, books, government documents, and other kinds of publications.
Note: Citations for sources that you read off of a screen are different from those that you read off of a printed page! Please look carefully at the links on the left, and use the "Electronic Sources" information, too.