Patent is an expensive but smart way to protect your business.
Getting a patent is not a quick and easy process. It usually takes years of prosecution (though you can claim "patent pending" from the moment you file the application) and thousands of dollars. However, the reward is a government sanctioned monopoly. Yes, MONOPOLY.
Patent is a deal you make with the public.
You discloses something other people don't know, and in exchange other people can't use it for a limited time period (about twenty years) unless you allow them. It's a win-win. You don't have to worry about someone else stealing your idea, and the others can learn and improve your invention.
It's not a contract.
Although the exchange of knowledge and a monopoly right is between you and the rest of the society, there's no contractual relationship between you and the society. Instead, the United States Patent and Trademark Office ("USPTO") issues a patent to applicants who discloses their knowledge in patent applications which meet certain requirements. Moreover, if someone infringes your patent rights, you don't go to the USPTO (nor to a law enforcement agency) but to courts.