Your game playing idea can't be protected without some form of fixed expression. In order to get a copyright, you must write the concept down. According to the U.S. Copyright Act, copyrights exist automatically in any "original works of authorship fixed in any tangible medium of expression," but copyright registration guarantees the fullest extent of legal protection.
Fixation and Registration
In order to register a copyright, you must "fix" your idea in a "tangible medium." Fixation can be as simple as jotting down notes or writing a short description on your computer. Flesh out your idea as much as you can; the more "expression" you have to show, the stronger your copyright protection becomes.
Save a duplicate copy of all of your fixed materials. This can be a photocopy, a hard drive file, or USB copy. It's important to keep your duplicates safe.
Register your copyright online with the U.S. Copyright Office at www.copyright.gov/eco/. Scroll down to "Login to eCO" and click on "Electronic Copyright Office." The site will prompt you to create a user registration.
Once you have completed your login profile, you can access the copyright application screen. Under "Copyright Services," click on "Register a New Claim."
Follow the prompts to complete your application. Register your game idea as a "literary work" if your description is written, as an "audio visual work" if your concept is a video game, or as a "visual arts work" if your game playing idea can be expressed mostly through sketches or drawings.
Pay the registration fee as prompted. It costs $35 to register.
Submit an electronic copy of your work. The Copyright Office accepts common file types like .doc, .pdf, .jpg, and others.