Copyright law, as defined in Title 17 of the United States Code, protects "original works of authorship fixed in a tangible medium of expression" for a limited period. The current period is the life of the author plus seventy years, last adjusted with the 1998 Copyright Term Extension Act.
Ownership of a copyrighted work includes the right to control the use of that work. Copyright protection gives the owner the exclusive right to make and/or distribute copies, perform or display the work, and make derivative works. Copyright protects the following eight categories of works: literary works, musical works, dramatic works, pantomimes and choreographic works, pictorial, graphic, and sculptural works, motion pictures and other audiovisual works, sound recordings, and architectural works.
An idea is not copyrightable, but if you put it in a recorded format (a "fixed expression of idea") and it meets originality criteria, copyright is automatic.
Use of such work by others during the term of the copyright requires either permission from the author or reliance on the doctrine of fair use. Failure to do one or the other will expose the user to a claim of copyright infringement for which the law provides remedies including payment of money damages to the copyright owner.
History of Copyright in 5 Minutes: " Copyright: Forever Less One Day" by GCP Grey