There are three very different terms being thrown around in this thread:
Trademark: A trademark protects a company or brand name or a logo. If you called your game, "Blackspoker Poker" you could file a trademark for that name. That
only protects you from people using
that name (or logo). You need to register a trademark with
The USPTO (or similar if you're not American).
Copyright: Copyright protects publishable works; text, images, recordings. Copyright protection applies as soon as a work is created. However if it's something you want to seriously protect, registering the copyright with The USPTO is a good idea. If you posted the rules of your game on your blog then copyright would protect your post. However, copyright doesn't protect
ideas just the specific expression of those ideas.
Patent: A patent protects an invention or process for 20 years. Patents are also filed with the USPTO where they undergo an approval process. In order to be patentable your invention must be new and non-obvious.
This can all be done by anyone, however, since you're asking this question here, if you're serious, you're going to need to consult with an intellectual property attorney.