The purpose of the hearing, known as an advisement, is to tell Holmes about the murder charges on which he is currently being held. A formal filing of charges by the district attorney's office will come later. Prosecutors could add to or change his charges in between.
Advisement hearings are typically short - perhaps only afew minutes - and may not even require the suspect to speak.
UPDATE: Here's video from CNN's live feed.
[There was a video here]