Databases are collections of articles. Depending on the database, articles may be from magazines, newspapers and academic journals.
Different companies (EBSCO, Gale, ProQuest) are database providers, so database interfaces (the opening search page) will differ in format from provider to provider, but will have similar 'limiters' - such as date/date range, full-text, peer-reviewed -- allowing you to customize your search.
Databases by the same provider can often be searched at the same time. For example, Academic Search Premier (an EBSCO database) can be searched at the same time as PsycINFO and PsycArticles and CINAHL as those are all EBSCO-branded databases. Searching more than one database at a time can be convenient and save time, when that is appropriate to the assignment (i.e, if a Psychology class assignment is to search for articles in PsycARTICLES, then search only that database).
Academic Search Premier - multidisciplinary database. Excellent resource for current events (news, politics) as well as science and medicine. Research articles including peer-reviewed articles are available in this database, but you'll also find plenty of information from newspapers, magazines and trade journals too.
CINAHL Plus with Full-Text - The Cumulative Index of Nursing and Allied Health Literature (CINAHL for short) is an especially important resource for nursing students. Some informational articles are available but most of the articles are research articles. Searches can be very specific to include articles with a nurse author - or to eliminate certain types of articles, such as systematic reviews.
PsycARTICLES - covers social and behavioral health topics. Most articles are research articles and linked to full-text.
PsycINFO - covers social and behavioral health topics. Many articles are research articles linked to full-text and are peer-reviewed.