If you're searching library resources, then the sources you'll find will probably be more useful than the sources you'd find searching the open web. That's mostly because almost anything can be uploaded to the open web, whereas something will generally only be purchased or added to a library's resources if a librarian or other qualified person decides it may be useful and adds it.
But regardless of where you find your sources, you won't be sure of what you've got until you spend some time evaluating them. By "evaluating sources," we don't mean determining whether they contain information that will help you prove a specific claim—that's a higher standard we'll consider in detail in the next module. No, what we mean is simply looking at your sources and figuring out what they can give you.