In the sciences, you often call something a primary research article if the topic is an original experimental study performed by the authors. In the humanities, a primary source is anything that is original to the time period which you are studying.
Whatever source you use, but especially sources you find online, remember to mindfully answer the three evaluation questions. History buffs abound, and they love to share their knowledge online--but there's no reason you should use an amateur historian's information on a website if better information by an actual expert or scholar exists elsewhere.
Quick reference for the three questions:
Vogel Library, Wartburg College | 100 Wartburg Blvd, Waverly, IA, 50677 | Phone: 319-352-8500 | Email: email@example.com