To answer the question, visit the Wikipedia page on Citing Wikipedia - it gives an explanation and examples for each major citation style, including APA, MLA and Turabian.
Be aware that Wikipedia may not be the best source of information in an academic paper. If the facts you are citing can be verified in another source (such as a book, an online reference book, or a journal article, a good strategy would be to use that source instead. One reason is that the purpose of a citation is to allow your reader to examine the evidence you used, and Wikipedia changes daily. Books and online reference books usually don't change.
Of course, there are times when it is appropriate to choose and cite Wikipedia. Wikipedia records many fascinating discussions about millions of topics, and you may want to refer to those controversies in your essay. The Williams College library web site has a good discussion of when to choose Wikipedia.
To create any kind of citation fast, try BibMe. To build a bibliography slowly with a long list of sources that you plan to reuse in later projects, check out RefWorks.
The UNLV Libraries web site has more style guide info, bibliography tools, and information on academic integrity.
