Once charges are filed, your friend will be served. He will need to go to court on the assigned court date and as a minor, he should be given a public defender.
Since he already admitted guilt, it is very unlikely the charges will be dropped.
His attorney can review the facts of the case and see if there is anyway to challenge his admission of guilt and get his statement suppressed. If there is no way to challenge the admission of guilt, it will likely be a very difficult case for your friend to win.