Copyrights cover a number of different things that may be important in your business.  The legalese description of copyrightable material is "original works of authorship," but a list of things that are, and aren't, copyrightable is probably more useful:

In the U.S., an author or creator of a copyrightable work acquires a copyright automatically, with no need to register the work or do anything else.  However, if the author wishes to stop someone else from copying the work, she must register it before filing suit.  If a work bears a copyright notice (like "Copyright © 2009 by Jane Doe") then the author may be able to get extra damages from an infringer.

The owner of a copyright is entitled to do a number of things with the work (and to stop others from doing those things).  The first thing that comes to mind, of course, is copying.  But the author is also the only person who can translate the work, display or perform it in public, or use it in a follow-up "derivative work."  It's quite common to sell or lease some of these rights to various people who want to do those things, and so copyrights can become a source of additional income.

One issue that comes up regularly concerns materials that one party hires another to create.  For example, a company might hire a photographer to shoot pictures for an advertisement, or a programmer to write code for a product.  It's critical that written agreements be prepared to cover this type of engagement -- copyrights can only be transferred in writing, and people often get burned when a disappointed contractor shows up, demanding additional money for the right to use the very same material he provided, and for which he was already paid.  Without  written agreement, you're often out of luck: pay up, or lose the copyright infringement lawsuit.