What does this actually mean to a newb

I am from the UK and I didn't understand indictments at first. It seems to work like this:

1. Discover a crime.
2. Find the perpetrators.
3. Present your evidence to a Grand Jury and ask if they think there is enough evidence to request a trial.
4. If they say there is enough evidence then the suspects are considered indicted.
5. Occasionally, there may be more people to catch and you don't want to scare them away by prosecuting your first suspect so they keep the indictment under wraps (i.e. sealed) until a more suitable time.