Copyright is a legal action where an individual can claim a work as their own creation, exclusive for their use. For example, Star Wars. George Lucas has the exclusive ability to use Star Wars for profit.
However, a work can be licensed. This is when a copyright holder and another party establish a deal that allows the second party to use the copyright holder's work. Ex. George Lucas allowing Disney to use Star Wars. (before he sold it to them)
Poster for the original Star Wars
After an amount of time determined by a government (typically the author's life plus 50 or 70 years) the work enters public domain. There anyone is free to use the work to their will, whether or not it is for profit.
Before the work enters public domain, however, outside creators may add a creative twist to a work to make it original. This is protected under Fair Use.
Poster for Spaceballs, a movie that is a satire of Star Wars
A fan parody of Star Wars
Many Public Domain Databases exist where users can find copyright free or expired content.
It is often argued that nothing is truly creative or original, with new works building off the old
A Photo comparing an older movie to a shot from Star Wars