Some of the information on the internet it is very good, some of it is not. Anybody can publish information on the web, which means you should use caution when citing any source you find online. A good example of this is Wikipedia - it is a good place to find background information on your topic but you probably don't want to use Wikipedia as a resource in your final paper.
For help discerning valid versus dubious sources on the Internet, please see the Criteria for evaluating sources