Copyright protection covers the expression of ideas; it protects you from having your works republished verbatim, or in modified form. It does not protect you from having someone publish the same idea in an original form. Copyright protection is available automatically for any work as soon as it is created, although you can recover more in damages if you register it.
- FAQs on copyrights are covered on the U.S. Copyright Office website.
Patent protection covers the working of inventions; it covers a means or process by which something is accomplished. It can be used to protect fundamental game mechanics; for example, there are two patents related to Icehouse, and there is a patent on the tapping mechanic in Magic: The Gathering. Patents must be registered with the US Patent and Trademark Office.
Trademark protection covers a name, logo, or other symbol that is used to represent a product, brand, or company. It protects you from having someone else use your name, logo, or brand to sell a competing product. It does not prevent someone from using the same name in a different field. Trademark protection is available as soon as you begin selling a product or offering a service under some particular name, although you have more protection if you register it.
- Patent and trademark FAQs can be found on the U.S. Patent & Trademark Office Website.
Creative Commons and other permissive licenses
With a Creative_Commons license, you keep your copyright but allow people to copy and distribute your work provided they give you credit -- and only on the conditions you specify here. If you want to offer your work with no conditions, choose the public domain. From here.
(Shpiel to come about how CC licenses are different from "public domain" and still allow other licenses to be issued by the copyright holder.)