How to sell a card game?

I've invented a card game and want to try and sell it to a game making company. What legal precautions do I need to take to keep my idea safe, and how do I go about trying to sell it? If a company likes it, will they buy the rights or something, or pay...

me royalties, or both? How does all that work?

well, Wizards Of The Cost are usually the main people to deal with for CGI cards.
Youll have to patent the idea fist (Contact your local coincil) the designs of the cards will have to copyrighted for the images etc. Then, approach a company such as adviseum or Wizards. They will buy the idea, but you will not be offered royalites since you would have to sell the idea including all patents to them.