A database is a collection of searchable information, such as articles, ebooks, films, etc. Most of the information has gone through the editorial process, so there is an expectation that the information is reliable and credible, and appropriate for academic level research.
CSN Library pays to subscribe to many databases, in support of various academic programs. Because the CSN Library pays to access these databases, they are freely available to CSN students, but not to others outside of CSN, which is why you must log in (when off-campus) to access the resources.
Search engines, such as Google or Bing, allow you to search the open web. Because anyone can "publish" information on the web, you must decide if any given piece of information you find is reliable or credible, and appropriate for academic level research.