There are different ways to search for academic journal articles. Academic Search Complete and JSTOR are probably the two most popular academic databases for undergraduates doing research.
Subject-specific databases help limit your search to a specific discipline. These are especially helpful for upper-undergrads. and graduate students.
Search It can help you access academic articles, however, it does not let you search with as much precision as more traditional journal databases. Watch out for book reviews too - they do not count as "academic articles" in the the most cases.
Google Scholar contains "non-academic" material such as newsletters, song lyrics, unpublished articles, and book excerpts from non-scholarly books.