When you get a paper assignment, your teacher might say to you, "Go to the library and get three sources for your paper from the electronic databases." When you go there, though, there is a pretty long list of databases, most of which have academic sounding names that don't tell you anything. For example, MasterFILE Premier or Academic OneFile. Huh? And how would you know what CINAHL means? (It means Cumulative Index to Nursing and Allied Health Literature, in case you're wondering.)
Well, here's a brief explanation. The databases listed under "General Magazine and Journals" are all large collections of general subjects- they have some of everything. Some of them have a focus- like Opposing Viewpoints and SIRS Knowledge Source, which focus on hot button issues like global warming and gun control. Some are owned by the same company, like MasterFILE Premier and Magill On Literature, so you can search them at the same time.
The databases under "Health and Science" are just that- health and science journals. If you're writing a nursing or psychology paper, look under this heading. Some, like PsycINFO and Psychology and Behavioral Sciences, are owned by the same company and you can search them at the same time too.
Then there are newspapers. So, if you want a new article from the New York Times or the Hartford Courant, it makes sense to go right there and search for it. The other databases might get it, but they might not have the most up to date articles. For example, Opposing Viewpoints gets current access to the New York Times, but as of 8:54 on April 15th, they only have articles from yesterday listed. The NYT database has today's paper already listed.
As you research and write papers, you get better at knowing which database to use. And you can ALWAYS ask your librarian (obviously).