In the United States, there are laws which protect people who are arrested for crimes. One of the laws says that the person who is arrested needs to understand that
- the police cannot force them to talk or confess their crimes
- anything that they say to the police will become evidence if they go to court for the crime
Because of this, poilce (or at least police on TV and movies) say this statement to a person who they are arresting:
You have the right to remain silent.
This means that the arrested person doesn't have to say anything. Then they continue:
Anything you say can and will be used against you in a court of law.
This means that what they say can become evidence in a trial against them.
There are other rights that the police usually read after that:
You have the right to an attorney. If you cannot afford an attorney, one will be provided for you.
These rights are a person's "Miranda rights". When a police officer says these words, they are "reading someone their rights":
I read him his rights and then put him in the police car.