Look for the information you need to cite a full-text article at the top or bottom of the page, or look for an option to click to prepare the citation in multiple styles. (The link might say "Cite" or "Cite this article.") Make sure to note the name of the database. Or use a bibliographic manager, so you can export the citation directly to your personal database of sources.
In The Scott Foresman Handbook for Writers, see the section on "Sources from library subscription services" for the style you are using. (In the library reference section at REF 808.042 R929s)