If the police think you pulled a diamond heist, and they have enough evidence to charge you with that crime, you'll be called to court for your arraignment, when you can plead guilty or not guilty. The trial comes next.
Arraignment comes from the French word aresnier, which means to address, or speak reasonably. It's almost only used in the legal sense as answering for yourself, or pleading, "guilty" or "not guilty." The verb arraign means to call someone before the court to answer an accusation (called in legal speak, an indictment), so an arraignment is either the piece of paper that calls you to court, or the hearing in which that charge is read to you.