Even if your only purpose is to summarize a short article, you need to give your readers publication or copyright information about that article. Typically, any piece of writing that refers to another publication includes a "Works Cited" page or a "Bibliography." Quotations and/or paraphrases also need to be cited through footnotes, endnotes, or in-text documentation. The proper way to cite this information differs according to your audience.
Note: If you're writing a stand-alone summary of an essay from one of your textbooks, check with your teacher about whether you need to turn in a separate "Works Cited" page. Teachers will sometimes forego this formality when you're citing only a single source that is known to the whole class.