"Trial by Jury" dates back to England, where individuals would be tried by a jury of their fellow peers/nobles. The United States adopted the standard in the Sixth Amendment of the Constitution. This amendment guarantees the rights that criminal defendants may have a public trial, a speedy trial (without undue delay), the right to know and face the charges and accuser, and the right to an impartial jury.
Jury duty is when an individual is summoned by the court to answer a questionnaire and appear before the court as a potential juror in a trial. In some instances, a summoned juror can be excused before appearing in court if sufficient cause/grounds are found by writing a letter and providing proof. For example, age, mental capacity, criminal convictions, no longer in the same jurisdiction as the court/venue, etc. It varies from city/state.
If you are summoned to appear in court for jury service, it is mandatory that you appear in court for jury duty. This does not mean you will definitely be on a jury or take part in a trial once you arrive in court. Failure to appear in court can result in a warrant out for your arrest and/or fines.
Once you appear in court for jury duty/service, you wait. If a courtroom requires jurors for a trial, the court will randomly select a large batch of jurors from the pool of jurors present for duty. The potential jurors enter the courtroom, and the process of voir dire commences.
Voir dire is the process that the judge and attorneys (prosecutors and defense attorneys) question/screen the potential jurors. The questions can range from asking if you have a conflict of interest in the case, a bias, etc. Depending on the answers, the judge and attorneys will eventually agree on a set of jurors to be sworn in for the start of the trial. They will also have a few alternate jurors in case a trial commences, and one of the original jurors selected is no longer capable of serving. This entire process can elicit a range of feelings depending on the juror. Some say it is a time-consuming process, others hate the idea of having to serve, and others do not mind.
The trial itself is straightforward from the juror's point of view. They hear the case presented in court, follow the instructions in the charge provided by the judge, discuss/deliberate among their fellow jurors, and render a verdict. In some instances, they are also charged with rendering a sentence after the trial should the defendant be found guilty.
If you have additional questions or need further clarification, please feel free to contact me to schedule a session.