An indictment is formally when charges 'stick' after being heard and voted on by a grand jury (which itself is mostly a rubber stamp - I've been a prosecutor for over a year and haven't had a single charge dismissed. Essentially the prosecution gets to 'cheat' at this step and all sorts of things unacceptable in a trial are fair game here and the defense doesn't get to put on a case - the standard of proof is also low)

From here things change depending on jurisdiction a little bit procedurally but ultimately the next step is more investigating where both sides start interviewing witnesses and broadly 'digging around' as the sides posture for either going to trial or negotiating a different resolution (ie a plea but in some instances things like civil compromise is seen as 'good enough' for the prosecution to justify dropping the case)

If it sounds like an indictment is nothing but a rubber stamp procedural thing thats because it is. It exists solely because the monarchy in England used to quite literally abduct people on charges with no basis in fact and hold them pretty much until they decided to let the person out (if they ever felt like it) so the indictment was created to force the crown to show that there was SOME evidence of the charges being alleged