Databases typically search for articles within journals. They also tell you what has been published, but not necessarily if we have it or not. Many articles are available in full text.
Some Useful Database Examples:
PsycArticles (full text)
PsycINFO (some full text)
Academic Search Complete (full text)
Newspaper Source (full text)
As opposed to databases…the library catalog searches for books and journals (as well as music, dvds, and e-books). An easy way to think of it is that it tells you what the library physically has…or provides for you. Catalog sources can be equally valuable.