If you are arrested, you have several fundamental constitutional rights:
Miranda rights: Before custodial interrogation, police must inform you of your right to remain silent and your right to an attorney. Anything you say can be used against you in court.
Right to an attorney: You have the right to have a lawyer present during questioning. If you cannot afford one, the court will appoint a public defender at no cost.
Right to remain silent: You do not have to answer any questions beyond providing basic identifying information. Clearly state: "I am invoking my right to remain silent. I want an attorney."
Right against unreasonable searches: Police generally need a warrant to search your home. However, searches of your person incident to arrest are permitted.
Right to a phone call: Most jurisdictions allow you at least one phone call within a reasonable time after booking.
What to do: Stay calm, do not resist arrest (even if you believe it's unlawful), clearly invoke your rights, and wait for your attorney before answering any questions.