WorldCat is a catalog listing library items at participating institutions across the globe. Many times, if you are trying to find an item that USC does not own, WorldCat is a reliable place to look to see if any library owns the item. From there you can place a request via interlibrary loan (ILL).
Databases are useful for searching for journal articles, newspaper articles, magazine articles, patents, etc. Most times when you use a database, you will be doing topic searching. The science database listed below, Web of Science, is a very powerful tool to search across various disciplines, journals, and years.
Topic searching is only as good as the topic being entered. Before you click search, utilize Boolean terms, like AND, OR, and NOT, to help refine your search. After clicking search, use refine results tools to help narrow down the number of citations.