What is the value of both primary source and secondary source documents in learning about world war ? is one better? are they the same?

OK so primary and secondary sources are very important and they shape history. The primary source is always better because usually it is like a newspaper or a picture or a book from that time period. Secondary sources are still important they are just not as reliable. An example of one is like someone saying that they saw something  happen but they could be lying. Or their perspective might  be slightly biased depending on their view.  

Explanation:

it would be that mali has the worst literacy rate than the others