I served once about 20 yrs ago. A lot depends on the state you live in, but here is what happened then
You reported to a jury pool(no diving board) room, where you sat until your name is called. (If your name is never called, you could stay in the jury pool for your entire service term, so if this is how they do it where you are, bring something to do, or something to read). If they call your name, they will send you, along with the others who names are called to a court room. They will then call 12 or 6 names (depending on the type of trial) frrm that group who go sit in the jury box. The attorneys ask them questions and can either reject or accept the Juror (each attorney gets a certain number of rejections) If a juror is rejected, they call a new name to replace them. Once they agree on a jury, everyone not chosen is sent back to the jury pool to wait again. My term was for two weeks and during that time I served on two trials (one criminal and one traffic).
If you get chosen for a jury, you will report to the jury room off the court room for the trial every morning for the duration of the the trial. If this looks to be a long trial, bring something to read or do, you might end up spending a lot of time in that jury room (and you won't be allowed to discuss the trial amongst yourselves.
In the criminal trial(drug case) I served on, there were three defendants, each with his own lawyer. Every time one of them objected, they would file us out of the court room so that they could discuss it.
It was an interesting experience but not one would like to repeat under the circumstances I was under. My employer at the time gave you paid jury duty, but subtracted any pay you got from the court from your pay. They also had a policy that any day you were released before noon, you were to report for the remainder of your shift. The problem was that I worked a swing shift, and the "powers that be" decided that in that case "noon" meant "before half of your shift was over" Since that was at 7:00 pm and we were always let go for the day around 5:00 pm, they expected me to come in and finish the last half my shift every day.
It was an hour drive to work, so I had barely time to get home, change clothes, get a bite to eat, and take off to work. I got off at 11:30, which, with a hour drive, got me home at 12:30 am. I would plop into bed in order to get up at 6:30 am, so I could shower, dress, eat breakfast and get to jury duty by 8:00 am.