Indictment and arrest are two major steps in the criminal justice system. One is an accusation, the other is an action.
An indictment is a formal statement of criminal charges. Indictments are issued, or "handed up," by grand juries.
Alternative to Indictment
An indictment is not the only way to charge someone with a crime. A prosecutor can file charges--known as a "complaint"--directly with the court. To "press charges" is to request that a prosecutor do so, and to agree to testify in court.
To arrest someone is to place him under direct control and custody, depriving him of liberty.
Courts can issue arrest warrants, but police can arrest a person without a warrant if they have "probable cause" that she has committed a crime.
Because an indicted person has already been charged, he will be arrested. But an arrest based on probable cause doesn't necessarily result in charges, and many arrested people are freed without charge.