A prosecutor has two ways of charging a felony to be tried in circuit court: (1) a criminal information. A grand jury indictment is a prima facie finding of probable cause that the felony was committed, and probable cause that the defendant was the person who committed it. If a prosecutor chooses to charge a felony in a criminal information, or if a  grand jury indictment has not been returned, a defendant has an absolute right to a preliminary hearing.
A criminal information is simply written charges written by the prosecutor. The prosecutor decides whether to bring charges.
The Fifth Amendment to our constitution says that nobody can answer for a crime “unless on a presentment or indictment of a grand jury.” That means that some formal process must occur before you have to stand for a felony tria.
If felony criminal charges are brought by a criminal information, there will usually be a probable cause hearing before a judge, called in Maryland a Preliminary Hearing. This is simply a hearing to determine if there is “probable cause” that a felony was committed.
2. A grand jury indictment:  The purpose is not to determine guilt or innocence, but to determine if there is enough evidence that some crime has been committed in order to have a trial later on.