You will usually want to use "scholarly" or "academic" sources in your research.  Why?

1. They're more credible and authoritative, since they're written by experts.
2. They tend to be more in-depth than popular sources, so that you can really understand the topic.
3. They'll lead you to other trusted sources.
4. Your professors will generally require it!

For information on how to tell if an article is scholarly or not, check Identifying Scholarly Articles

Open the two links below, and compare the two articles.  List the differences between them.