My knowledge of Copyright isn't extensive as most lawyers but was along the lines of most peoples, if something is under copyright, it generally means that it's protected and shouldn't be stolen, re-created or have anything done to it that would effect it itself.
While that might sentence might not make much sense, I hope you can see that copyright literally means it's protected. And that's basically it.
You're probably thinking, what is fair use? And can it do anything with copyright?
Indeed it can, Fair use has certain definitions as to what it is and when it can be used. For example, You know YouTube? The massive video sharing website? Yea that thing, fair use is pretty big on YouTube due to the amount of content being uploaded every second and consumed the other second.
In a nutshell, fair use is any copying of copyrighted material for the intended purpose of commenting, criticism, parodying or any sort of "transformative" process...
And that's how Stanford University Libraries tried to define "transformative"
But be aware, if you attempt to publish content that uses copyrighted material and doesn't fall into the above intended purposes. You will NEED permission from the copyright owner in order to do so, or you could be faced with DMCAs, a form of take down demand for any unlicensed use of material on the internet, or even legal troubles...
For the YouTube example above, YouTube has employed a somewhat robust system at finding copyrighted material, flagging the video and notifying the uploader of the discrepancy. I say robust because the system isn't perfect has been abused countless times by publishers taking down content that was without a doubt within fair use.
As for a non-YouTube example, well you don't have to go far to find a game in development that seems be a parody of another game/series but a closer look says otherwise.
In this case it's a Star Wars game, you can already hear Disney's lawyers ready to pounce on it, that it simply titled Galaxy in Turmoil. What's interesting about this is that Steam/Valve signed an agreement with the studio to publish the free to play title on Steam.
From what seems to be an in-engine screenshot. Taken from Frontwire Studios
Is the game a breach of copyright for using the Star Wars IP without permission from Disney or EA (EA acquired the rights to publish star wars games)? Or does this fall into fair use since it could be labelled as a parody of of the Star Wars Battlefront series?
Time to sit back and watch...