Questions and criteria you need to consider for any source you want to use. In order to find a credible source you need to dig through the web and review different criteria to ensure it meets quality standards.
Download the documents your librarian asks you to download.
No one else will make sure you find credible/reliable information online except you, so be picky about it!
At the bare minimum, make sure you can identify the following things on a web site:
the date it was posted/updated
who wrote it (bonus points if you can Google that person/organization to see if they're a credible source of info)
why the info on the site was written (is it opinion, persuasion, or just informative? Check the site's "about us" section)
Here are some more in-depth questions you can ask yourself to figure out whether you're looking at a high-quality web site: