A little easier to understand the significance:

A grand jury has ruled that the evidence presented is sufficient enough to warrant a trial to determine if a crime has been committed.

Typically grand juries are either random citizens (selected via jury duty), or volunteers within the community, depending on the city rules. They are not elected positions, nor are any legal qualifications required. It’s simply high level evidence, and descriptions of laws that may have been violated.

It’s not an indication of guilt, just that there’s enough of a question that is worth holding a trial to determine guilt.

Edit - at least, that’s what a grand jury usually is. I wouldn’t be surprised if federal charges on a former president requires more qualified grand jurors than the baker down the street, or retired carpenter with time to kill that comprises your typical grand jury