There are four ways to protect ideas: Patents, Trademarks, Copyrights & Trade Secrets.
If the essence of your idea resides in both structure and function and your idea involves a machine, manufacture, composition of matter, process or an improvement of one of these, then you can file for a UTILITY patent. Utility patents require a patent application be filed with the U.S. Patent & Trademark Office (USPTO) with a detailed written description, usually including drawings, of how to make and use the invention and with "claims" which legally define the subject matter your invention. An Examiner in the USPTO will then examine your patent application for novelty, unobviousness and utility. If allowed, your utility patent will protect the structure and function of the invention as these are defined by the claims.
If the essence of your idea resides in the novel appearance of an object, you can file for a DESIGN patent. Design patents require a patent application be filed with the USPTO with very detailed, formalistic patent drawings. Your patent application is then examined by an Examiner in the USPTO for novelty and obviousness over prior art. If allowed, your design patent will protect only the ornamental appearance of the object, not its function and not its internal workings.
If the essence of your idea resides in a symbol or a name, you can file for trademark protection. A trademark is given for names and symbols which identify goods or services, not for the names of the companies providing them. As an example, "Cheerios" is a trademark, but General Mills, Inc. is a company name. Trademark ownership arises with use. However, if you want to put everyone on notice of your trademark ownership, so that there is greater likelihood of incontestability as to whether you own it, then you will want to register with your state or with the U.S. Patent & Trademark Office (USPTO). However, you can only register with the USPTO if you transact business across state lines or internationally. Trademark applications are examined as to its degree of fancifulness and to what extent the name or symbol is confusingly similar to another name or symbol in the same channel of commerce.
If the essence of your idea resides in artistry, such as a written work, a visual display or artwork, a musical score, or a videotape or an audio recording, then you should protect yourself by copyright. Copyright protection immediately comes into existence the minute you complete your work in fixed form - you do not have to register with the Register of Copyrights in Washington, D.C. in order to enjoy protection. However, you must register if you are directed to do so by the Register of Copyrights or if you want to institute suit against an infringer. Registering a copyright is ordinarily simple, as there is no copyright search and examination is usually limited to basically formal matters. Copyrights protect the expression of an idea, not the idea itself.
If your idea resides in commercially valuable secret information, you can protect your idea, whatever it is, by simply keeping it secret. A "trade secret" is protected by state law. In order to keep your idea secret, whenever you discuss it with anyone, make sure they sign a non-disclosure agreement first. The formula for Coca Cola is a good example of a successful, long-lived trade secret.