The music business is built upon, and exists because of copyrights. Anytime anyone creates an original song, and either writes that song down or records it, a copyright is created. Along with the creation of this copyright comes a bundle of rights that the creator immediately has. The creator can, for example, sell or license her copyright to someone else. In a nutshell, that's the music business: someone creates a copyright, allows someone to use it, and then derives financial compensation for that use.
Of course, this process of allowing someone to use a copyright and the actual use of the copyright can result in any number of complexities, but at the core there is simply the copyright.
To be a successful artist in the music business or to be a successful business person in the music business you MUST understand how copyrights work - they are the currency of the record industry. This section will explain them.