What we usually mean by property – physical things which we own – is called real property to distinguish it from intellectual property. Real property – things that actually exist, like cars and sandwiches – is easy enough to understand, and we’re mostly familiar with the ways its ownership can be transferred: it can be sold outright, sold in part, rented or leased (you wouldn’t want to rent a sandwich, but legally there’s no reason why you couldn’t.) Intellectual property, on the other hand, is more complicated. For one thing, not everything we can think of or imagine can be intellectual property. An idea, for instance, is not yet property; we have to take the time and effort to turn that idea into some kind of product. This does not have to be a finished product – a film script is intellectual property, even if the film doesn’t ever get made – but it needs to show that the creator has made an original work. This is a key point, because in most countries all intellectual property is automatically copyrighted.
What does that mean? It means that it has become property that the creator owns. That creator now can control what is done or not done with the property – whether and how it is copied, adapted, sold, etc. – and can sell or lease any or all of those rights as he or she chooses. Each time something substantially new is done to the property, so long as it is done with legal right, a new property is created and a new copyright established.
Most countries have their own laws relating to copyright, but nearly all also follow the Berne Convention for the Protection of Literary and Artistic Works. The Convention requires member nations to recognize copyrights that are established in other members’ countries (so you don’t have to establish a separate copyright in each country in the world), makes copyright automatic (so copyrights do not have to be registered, although some countries such as the United States provide added protection to registered copyrights) and sets fifty years as the minimum time before a copyrighted work can pass into the public domain. 
The most significant national laws relating to copyright are Title 17 of the United States Code which lays out American copyright law, and the Copyright Act, which defines copyright in Canada. Both of these laws cover:
- what kinds of works can be copyrighted
- legal protections for copyrighted works
- differences in how copyright applies to different media
- how copyrights can be sold or assigned
- what government bodies administer copyright
- when copyrighted works pass into the public domain
As well, many copyright laws (including the Copyright Act) give moral rights specifically to the creators of a work. Unlike other aspects of copyright, these moral rights do not automatically pass on to the new owner of a copyright: in Canada they include the right to have your name or chosen pseudonym associated with the work and the right to protect the integrity of the work. (For instance, the artist Michael Snow was able to prevent the Eaton Centre from adding scarves to a sculpture of geese he had sold them.) 
Generally, if you want to do anything with a copyrighted work beyond its intended use, you need to get the permission of the copyright holder or someone acting on his or her behalf. (For example, you do not need permission to read a book, but you do need it to turn the book into a play or a movie; you don’t need permission to listen to music, but you do need permission to play it in a public place.) However, there are important exceptions: fair dealing (in Canada and other Commonwealth countries) and fair use (in the United States) grants certain rights to use copyrighted works without needing to get permission from the copyright owner. Both fair use and fair dealing are affirmative defences in law, which means that neither one can prevent the owner of a copyright from suing you for infringement: if you are sued, you have to prove in court that your work falls under your country’s definition of fair use or fair dealing.
Of course, the owner of a copyright may release the work to the public domain at any time he or she chooses. Copyright owners can also release works under licenses that are less restrictive than copyright law: for instance, there are a variety of Creative Commons licenses that let creators grant permission to copy or transform their work without giving up copyright, and may also place limitations on that use (for instance, that they be listed as the creator of the original work, or that all use of the work be for non-commercial purposes.)
While copyright issues go back to the time of Shakespeare, recent technologies have made an understanding of copyright necessary for our daily use of media, particularly music and movies.
*Note: This information is NOT intended as legal advice. If you are facing a legal issue dealing with intellectual property law, consult a lawyer.
 Berne Convention for the Protection of Literary and Artistic Works. World Intellectual Property Organization, 1979. http://www.wipo.int/treaties/en/ip/berne/trtdocs_wo001.html
 Trosow, Samuel E. “The copyright policy paradox: Overcoming competing agendas in the digital labour movement,” Ephemera 10, 2010.