My friend has been arrested. Now he's being told he has an arraignment and a preliminary hearing. Aren't these the same thing? When can he get out of jail?

No, they are not the same.

At the arraignment, your friend will appear before a judge who will tell him, officially, of the charges. At the arraignment, bail will be set, or possibly reduced if previously established. Your friend may be released on his own recognizance. If he's in need of an attorney and meets the guidelines for court appointed representation, a public defender will be assigned. If the charge is a misdemeanor, some courts allow a plea to be entered at this time.

At a preliminary hearing, the district attorney must establish for the judge that there are reasonable grounds (evidence) to proceed with the charges and bring your friend to trial.

Getting released from jail will depend on:

  1. The charges
  2. If there is bail
  3. Whether or not the defendant can meet bail