Online resources can be useful for contributing to your research. Especially when researching older information that might be in the public domain. You'll be surprised what you can find digitized and freely available online! The thing to remember about online resources is that you are responsible for verifying the credibility of the source. Ask yourself a few questions like:
Watch this three minute video from NC State University that addresses these three questions: What does it mean for a source to be credible? Why is it important to use these sources? How can you tell if a source is credible?
If you need help evaluating a web source, ask a librarian for assistance.