On, Facebook or Twitter, look under the headline to see the address of the website this information comes from. In your web browser, look at the address bar to see the full URL of the website.
If the site has a strange or unfamiliar name, stop right there and search for the same story on Google or elsewhere to try and get information from a source you trust. If it doesn't show up anywhere else, that's a big problem.
Also be aware that fake news sites sometimes have domains that are very close to real news sites, such as the fake ABCNews.com.co instead of ABCNews.go.com.