Library databases are collections of materials allowing you to search for information in an organized collection, leading to more relevant results. Content in databases has usually undergone some sort of review process, so the material is more reliable than information found on the Internet.
Google Scholar is a search engine that specifically searches scholarly literature and academic resources. Unlike Library Databases (which contain resources chosen by people), Google Scholar results come from an automated search of the internet that is then limited to scholarly material. Because it is automated, results should be reviewed carefully as some aren't scholarly (for example, a high school term paper). Google Scholar is a great option if you aren't finding information about your topic in library databases.
Search engines, like Google, use bots to search the Internet and find results that match the words you entered. Search engines are great for finding background information as well as information on groups and organizations but it is difficult to narrow your search - and you'll often get thousands of results. In addition, anyone can post anything to the web.