According to the U.S. Copyright Office, copyright is "a form of protection grounded in the U.S. Constitution and granted by law for original works of authorship fixed in a tangible medium of expression. Copyright covers both published and unpublished works." Copyright owners have exclusive rights to reproduce, distribute, perform, publicly display, or make into a derivative work. If anyone else wishes to do any of the above activities, they must first ask permission of the copyright owner.
What works are covered by copyright?
Copyright covers "original works of authorship including literary, dramatic, musical, and artistic works, such as poetry, novels, movies, songs, computer software, and architecture. Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed."
What is fair use?
The fair use doctrine allows portions of a work to be used without permission for the purposes of commentary, criticism, news reporting, and scholarly reports. You must always cite your source however.
How much can I copy under fair use?
Fair use guidelines do not stipulate how much of a work can be copied. A good rule of thumb is to use the smallest amount possible that still conveys the needed information.