Important note
Automatic citation helpers (e.g. EndNote, Zotero, EasyBib, etc.) must ALL be used carefully. They are usually not 100% accurate. If the data about an article or book is input incorrectly (as it often is), the citation generator does not "know" how to fix any errors. Always check your entries against the manual.
How Citation Managers Work
Most citation managers can automatically import bibliographic data for each of your sources into their program, and the program will usually work together with your word processing program to auto-generate citation within your document. You can also input citation manually.
Citation Helpers in Databases
Many database provide a button or link to generate a citation of an article in several styles. Look for a link or button that says "Cite" or "Cite this item." These operate on the same principles as above: they are auto-generated and often not 100% accurate. Use them to start your citation, but be sure to check them for accuracy.