Most works are protected by copyright
Almost all creative and intellectual work is protected by copyright. Remember that facts are not subject to copyright.
Copyright is automatic
Works do not have to have copyright notice or be registered in any way in order to be protected by copyright. This means that everything from a novel to a napkin doodle has full and automatic copyright protections.
Copyright lasts a long time...
Works are protected for the life of the author, plus seventy years. If a work was "made for hire {PDF}" It is protected for 95 years from the publication or 120 years from the creation of the work (whichever is less). The rules are different for works made before 1978 and incredibly complicated.
...but not forever
Works with expired copyright pass into the public domain and are available to be used in whatever way you'd like. Also not protected by copyright are works created by the US government (and some states), facts, ideas, and methods.
