Do I have to talk to the police?
You do not have to say anything to an officer to assist him in making a case against you.
The police can stop you in the street and talk to you. You do not have to, and should not, answer.
The only person who can force you to answer questions is a judge, and then only in limited circumstances. Those circumstances only occur in a courtroom. The street is not a courtroom. A cop is not a judge.