Zotero is a free software program. It does more than just generate citations -- it also helps you keep track of the books and articles that you've already found. The UMW Libraries recommend Zotero for all students.
If you don't want to download Zotero, you can still use some of its basic functions in a browser-based tool called ZoteroBib.
Most of the library databases include built-in tools that generate citations automatically. To find these tools, first click on any one item in the database (such as a book or an article). Then, look for the word "Cite" or "Citation." It's usually somewhere on the right-hand side of the page.