I am amazed by the amount of people who have no idea how a NDA works. I'll try to explain it in simple terms so that these people who have no idea how NDAs work will now understand.

A NDA is a non-disclosure agreement. That means that two parties have signed an agreement to not disclose certain information. This information can be anything, but usually it's related to employers. Employers often have their employees sign a NDA to protect certain information about the company - business plans, trade secrets, that sort of thing. In order to work for the company, the NDA must be signed. If it isn't signed, then the employee doesn't work for the company.

Now, I do see that many celebrities are making use of these NDAs regarding personal relationships, and while it might seem suspicious, it is completely legal. Celebrities don't want private information about them getting out into the public, so they'll have their partners sign a NDA. If things go bad and the relationship ends, the celebrity will pay the partner to not talk about their relationship with the press. Because people are liars and they will lie about anything and everything, these NDAs might be essential to stop libel, slander, and defamation of character. 

Here's something that is very important to remember - NDAs are legally binding contracts! If you sign one, then you decide to tell everyone what was in the NDA, you have violated the terms of the NDA and legal remedies may be sought. If you received money as a part of the NDA, you will have to pay that money back. If you were employed as part of the NDA, you will lose your job. 

Here's another important thing to remember about NDAs - you can't use a NDA to cover up a crime. For example, if you witnessed a murder, the murderer can't buy your silence and make you sign a NDA to not go to the police. No court will ever accept a NDA that was used to cover up a crime. No attorney will ever advise their client to sign a NDA that was used to cover up a crime.

Always consult an attorney before signing a NDA. Also, make sure you understand the penalties that you could face if you ever violate the terms of a NDA.