Many of the books and articles you find through the library are considered "scholarly," which means that they have undergone a lengthy review and publishing process. Compare this to the open internet, where anyone can publish anything regardless of their credentials.
This video from the University of Southern Australia summarizes how to use the CRAAP test to evaluate resources.
The CRAAP test is a list of questions that you should ask when evaluating information. Familiarize yourself with it before starting and review it as needed as you conduct your research.
Your job as a researcher is to find out what experts (people with advanced training on a topic) have concluded about your topic and use that evidence to make an argument. The most credible resources are those written by experts and "peer" reviewed by other experts.
For more on determining credibility, check out this video from North Carolina State Libraries.
The CRAAP Test is a great way to do some basic evaluation of a source. But often when you're evaluating a webpage, CRAAP is not enough because you can't find all the information you need on the page itself - you need to leave the page and do some additional research about the organization, the author, or the claims being made.