If you are looking for an article and you know the title of the journal that its from, look for the journal title using the University Collections search in StarPlus. Use the Cardiff Index to Legal Abbreviations to find the title of the journal if it has been abbreviated at http://www.legalabbrevs.cardiff.ac.uk/.
If you want to find journal articles about a particular area of the law, you should use Lexis Library, Westlaw UK or HeinOnline.
Now test yourself on finding secondary legal materials. Take the quiz.