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 posted 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 ” it is protected for 95 years from 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. Try this copyright slider from the Copyright Advisory Network when in doubt.
...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.
Copyright is seen as a bundle of rights. These rights include the right to:
Because these rights are imagined as a bundle, the owner of the copyright can give away, sell, or otherwise license some or all of these rights to others (as when an author negotiates a contract - they may give the publisher the right to copy and distribute the work but not make future derivative works, for instance).
Copyright only applies to the following kinds of works:
This list encompasses most kinds of creative or intellectual expression. Works must also be "fixed in a tangible medium of expression". Unfixed works like improvised music, speeches, or dances are not protected by copyright.
Remember: copyright is not designed to reward hard work but, rather, to foster creativity. Works that took a lot of effort to put together but that don't contain original expression do not qualify for copyright protection.