Depends a lot on what it's for. High school might find it acceptable, college less so. Research suggests primary sources usually. I'd be more inclined to want you to find out what sources History.com used to create the presentation and go to them. Secondary sources are usually more for historiographical works, or for general information that isn't central anyway. How you cite it depends on what you're using; APA, Chicago, MLA, etc. Also where you're citing; footnote, parenthetical, bibliography, etc.