Library databases are online collections of resources and can include a variety of formats as well as levels of quality. There are general databases such as the Quick Search and discipline specific databases such as IEE Xplore.
General databases cover most subjects and index a variety of publications including scholarly (or peer-reviewed) journals, newspapers, and magazines. Subject specific databases specialize in a subject area and tend to include scholarly journals and books.
You may need to find specific types of sources, such as patents, standards, or conference proceedings. Certain databases focus on the type of resource, as well as they discipline.