A database is a collection of information on a website organized so you can conduct a search (by keyword, title, author, etc). The UML Library provides free access to a multitude of databases for students which have sources that include journal articles, books, conference papers, maps, government reports, etc.
It's a good place to start to look for articles, books, etc. Especially peer-reviewed articles from academic journals (for example, Andean Geology or Lithos). To clarify, a database can be used to search for journals, which contain peer-reviewed articles, vital to references when writing a thesis or doing research.
Some databases provide full-text and some don't. If the database you're searching doesn't include full-text, use: