When you're accused of a crime, you may know that an arresting officer could read you your Miranda rights. Is the officer always required to do so at the point of arrest? No, and that's when it becomes tricky.
When you're under arrest, the best thing you can do for yourself is to stay quiet and respectful. The Fifth Amendment gives you the right to stay silent and say nothing that could incriminate you. Those rights are technically offered to everyone, but the police need to let you know about those rights only before you're being questioned.
Here's an example. If an officer takes you into custody and is casually talking to you in the car, you may not need to be read your Miranda rights. The officer isn't questioning you, so there is technically no risk of incrimination. Most officers do tell you your Miranda rights immediately to protect themselves; if they hear you give evidence or a confession, they want to be able to use it in court without the risk of the case getting thrown out.
If you go through an interview and questioning without anyone telling you about your Miranda rights, that's a problem. It's a requirement for you to have your Miranda rights read to you before questioning. At that point, you're told you can stay silent, ask for an attorney and that anything you say could be used against you in court.
It's in your best interests to ask for an attorney if you're arrested. Stay quiet and wait for help on what to do next.
Source: FindLaw, "'Miranda Rights' and the Fifth Amendment," accessed Feb. 08, 2018