Copyright limits who may legally use or make copies of a work.
Ideas cannot be copyrighted, only works that are fixed in some way.
Using or making copies of a work you do not own the copyright to requires permission, and often payment.
Fair Use allows the copying or use of copyrighted work without permission, under certain circumstances.
Fair Use allows copying for education, scholarship, criticism, parody or satire, and transformative works.
Fair Use is a legal defense, not a law, and cases are evaluated individually. Evalualtion is done by examining:
Professor Eric Faden of Bucknell University created this video on copyright law.