When an individual is detained by the police, that individual has certain constitutional rights. And, after Miranda v. Arizona, 384 U.S. 436 (1966), the detained individual has the right to be informed of those constitutional rights. Namely, the police are required to say something that sounds like this:

You are under arrest. You have the right to remain silent. Anything you say can and will be used against you in a court of law. You have the right to an attorney. If you cannot afford an attorney, one will be provided for you. Do you understand the rights I have just read to you?