Does Fair Use give me free reign to reuse any material I want without getting permission?
No. “Fair Use” isn’t a magic phrase you can invoke to excuse your use of someone else’s creative work under any circumstances. To be clear: you can’t copy someone else’s work and then simply claim fair use.
What is considered “fair use” depends on the circumstances? To oversimplify for a moment, fair use protects creators who reuse copyrighted content in a few ways: when the new work directly critiques and comments on existing works; for educational or scholarly purposes; to transform the source material into something new. Of course, it’s a bit more complicated than that, so please read on before deciding whether you can claim fair use.