Here is how the article below would look in MLA format in your "Works Cited" list at the end of your paper. As you can see the format for an article citation is different from the format for a book citation:
Beliveau, Richard, and Denis Gingras. "Green Tea: Prevention and Treatment of Cancer by Nutraceuticals."
Lancet 364 (2004): 1021-22. Academic Search Premier. Web. 17 July 2016.
Here is the publication information for this journal article as it appeared in the Academic Search Complete database when it was retrieved on July 17, 2016:
Note that for online articles you have to give information not just about the original journal where the article was published, but also what database you got it from, the medium of publication, and when you accessed it. (The same article might be available in more than one database.)