So you've got a great idea and you want to make sure you get credit—and any potential revenue—from it. Unfortunately, you can't trademark, copyright, or patent an idea. In order to protect something, you must first make it tangible. Instead of an idea, you need an actual invention. Inventions can be patented.
First, let's look at the words trademark and patent. A trademark is a name of a product. If your invention—not your idea—has a name, you can apply to have that name trademarked so that only you can use that name. For example, Kleenex is the trademarked name of one brand of tissue. Nobody can use the name Kleenex on a product other than the company that owns the trademark. Other companies can still make tissue, however.
A patent protects an invention. In the United States, you don't need an actual invention to file for a patent. You do, however, need to be able to explain that idea in enough detail that the actual invention could be developed. It doesn't have to be developed, but your plan must assure the patent office that it could be developed.
Some people believe erroneously that you can patent an idea by simply mailing it to yourself. In theory, the postmark on the envelope proves when you came up with the idea. However, this is a myth. First, this envelope must have a postmark, and not all do. Second, the envelope can never be opened without losing the claim. Third, if someone else comes up with the same invention and you try to make a claim against them, you could be in trouble for lack of diligence, suppression or concealment, or abandonment.
The only way to protect an idea is to first develop a concrete plan to put the idea into a tangible product, and second to file a provisional patent application. If you wish, you can also trademark the name of the product, but this involves making sure no one else is using the name, and then filing for your trademark. This should be done with the help of an attorney.
There is one way to protect your idea without a patent. If you can get someone to sign a confidentiality agreement stating that they will not use your idea without your permission, then you have protected your idea. It's easier said than done. Just having a friend sign such an agreement is not enough. You need to get manufacturers, suppliers, or investors to sign and many are unwilling to do this. Since signing gives you the rights to sue if they develop a similar product, even if yours never gets beyond the idea stage, few people are willing to sign something that leaves them exposed to liability.
So, it all comes down to the patent. But to get a patent, you need an actual product, or at least a clear definition of one. So to protect your idea, design the actual product, at least on paper, and file a patent application. Until you have that application filed, anyone can take your idea, invent an actual product, and you have no legal recourse.
Your best bet is to talk with an intellectual property attorney about your options.