Keep in mind:

1. Who created the website?
2. Who is the intended audience?
3. Where did they get the primary sources from?
4. Is the content clearly explained, organized, and accessible?

According to the Library of Congress, "Primary sources are the raw materials of history — original documents and objects which were created at the time under study. They are different from secondary sources, accounts or interpretations of events created by someone without firsthand experience.”

Primary sources provide direct, firsthand evidence about an event, object, or person. They are not interpretative beyond that original perspective. Primary sources include everything from diaries, letters, manuscripts, audio and video recordings, speeches, artwork, interview, surveys, emails, scientific research results, census records, etc. 

Secondary sources is a secondhand account or interpretation of an event, object, or person. They describe, interpret, discuss, analyze, evaluate, and interpret primary sources. Secondary sources are often published works, such as textbooks, documentaries, journal articles, and nonfiction books. Also includes interpretations of the significance of data sets, book or movie reviews, etc.

It can be difficult to tell the difference between primary and secondary sources. For example, some materials might be considered a primary source of one topic but a secondary source for another. For example,  a biography about Amelia Earhart might be a secondary source for a research project about Amelia Earhart, but a primary source for a research project analyzing how historians have interpreted her life.