The state can't (in theory, at least) arrest someone or place someone on trial absent probable cause,
i.e., reasonable grounds to believe that a crime has been committed and that the suspect did it. A grand jury's job is to determine whether probable cause exists. A true bill, commonly known as an indictment, is a GJ determination that probable cause exists. A no bill is a determination of no probable cause.
A GJ indictment doesn't necessarily guarantee a prosecution. The prosecutor still has discretion not to pursue the case. If the prosecutor decides to go forward, it's up to him or her commence a criminal proceeding by filing the indictment in the appropriate court.
Every state in the U.S. has some form of grand jury system, but only about half require a GJ indictment as a condition precedent to commencing a prosecution. Depending on where you are and the crime at issue, a judge can make the probable cause determination post-arrest following an evidentiary hearing.
Finally,
@filing a false report = "disorderly conduct" in Illinois.