Sometimes a database will give you the option to cite an article. Other times, you will need to create the citation yourself. Even if you don't know how to cite a source the minute you look at it, email it to yourself (or write down everything related to author, title, publication date, whether you found it in print, or online) so that you can work through citing it later.
A citation manager helps you
Zotero is a free, open source citation manager that makes it easy to save articles, websites, and other research sources.