I served on a jury last year.
The way it works in our county is that you are sent a questionnaire to fill out. Then you show up for your week (typically) of jury duty. You sit in a large room with all of the other potential jurors and wait for a case to come along. When a case comes in, a pool of about 20 to 30 or so jurors is chosen at random. Since it is random, it’s entirely possible to go in there for an entire week and never get called. However, if you serve on a case and that case ends, you go back to the room with the other potential jurors and, again since it is random, you can get called again. So some folks never served on a case and some folks served on more than one.
When I got picked for a pool, we went up to the courtroom and were all seated according to our juror numbers. At that point the prosecutor and defense both got to ask us a bunch of questions. Typically it was “does anyone have a family member who works in law enforcement, if so raise your hand” with various other questions and people would raise their hands accordingly and each side would note which jurors raised their hands to each question. In our case, the questions weren’t all that probing or intimate. They did ask about our opinions on illegal drug use, legalization of marijuana, and stuff like that. I got the impression that refusing to answer wasn’t an option. I suppose that if you were the type of person who illegally uses drugs some of those questions might have been uncomfortable. One woman did admit that she saw absolutely nothing wrong with people illegally using drugs no matter what the law said.
After that, the prosecution and defense took turns crossing people off of the list until they whittled us down to 12 jurors. Everyone else was sent back to the main room.
Once it was just the 12 of us, only then did we find out who the defendant was and what the case was about. In our case it was possession of drug paraphernalia and possession of a weapon by someone who is not allowed to possess a weapon. Basically, the police raided a crack house and this guy was there with a crack pipe sitting on the table in front of him, and when they searched his apartment upstairs they found a gun (he’s a convicted felon). We were given instructions about what the law was, the meaning of possession (there’s two types - one if you actually have the thing in your hand, the other if it is under your control but not on you personally - the example the prosecutor gave was his notepad was his possession even though it was in his office on his desk and he was here in the courtroom with us). We were also told that the prosecution and defense would present evidence, but those were not facts. It was up to us to determine what the facts were.
We found him guilty on the drug possession but not guilty on the gun possession since there were other people that lived in the apartment and a bunch of drug dealers and users constantly going in and out of it and the gun really could have belonged to any one of them.
We got picked for the pool at about 10 am, were whittled down to 12 jurors before noon, took a break for lunch, and the trial ended around 4:30 pm.