A trade secret is that idea or recipe kept secret by a company but used to further the company's business. The most well know example is the secret recipe of Coca-Cola. The fact a trade secret exists does not have to be protected, but the contents of the trade secret must be hidden. Therefore, any registration process would be highly counter productive. If a trade secret is valuable because it is secret, the registration which asks what is being protected destroys the value of the trade secret.
While a trade secret is not registered, that does not mean there is no protection. However, trade secrets, like any other source of intellectual property grant a constructive monopoly over the idea. It is possible to sue and prevent the spread or use of a stolen trade secret. You just have to be careful to ensure the trade secret is put under seal and protected through the court process.
As seen with Coca-Cola, a trade secret can be a recipe. Indeed, unlike the other forms of intellectual property, a trade secret can be a broad scope of things. Patents are for engineering feats primarily, copyright is for the written word and art, and trademarks are identification symbols of a company. While a trade secret could be converted into a patent, trade secrets tend to be "everything" else. A chemical formula for a brand of de-icing salt. A the code of a computer program. A particular method to building a product. All of these could be trade secrets if treated the right way.
A big part of trade secret law is in the name. A trade secret must be kept secret. If every single person in an business knows the secret, you may have a problem. Now, if it is you and one or two other people, the idea is probably still secret. If there are thirty or more people, then there may be a problem. However, it depends on the secret to be protected and the reason all the employees know the secret.
As a general rule, trade secrets are helpful because they give you a competitive advantage over your competition. However, in the realm of trade secrets, silence is preferred.