(a) When a grand jury is impaneled and sworn, it shall be charged by the judge who summoned it. In so doing, the judge shall give the grand jurors such information as the judge deems proper and as is required by law, as to their duties, and as to any charges of crimes known to the court and likely to come before the grand jury.

(b) When the grand jury has been impaneled, sworn and charged, it shall retire to a private room, and inquire into the crimes cognizable by it.