Great question! A good source is authoritative and relevant to your topic.
Relevancy means the source helps you answer your questions, learn widely about your topic, and think about your topic in new ways.
"Authority" and "credibility" are pretty interchangeable when talking about an information source, but they are trickier to determine. Some evaluative questions to keep in mind include:
- Is this information deliberately biased, and is that a good or bad quality?
- Who wrote it? Are they an expert?
- When was it published? What is the publication, and does that publication have a good reputation?
- Why was it published: to inform, persuade, entertain, etc.?
- Does it cite its sources? Does that matter for your intended use of the information?
Ultimately it is up to you to determine, using research and your own critical judgment, whether a source is authoritative or not. And "credible" and "authoritative" can mean something and look different to everyone. Your instructor expects you to use credible, authoritative information on your research essay, so be upfront and clear about why you trust the information your choose to use.