I've been called for jury duty 4 times over the last 8 or 9 years. I LOOOVE it. I know that sounds nuts, but that have this place called The Quiet Room, where there's not TV, no radio, no cell phones, and very, very little talking. I bring a book and some cross stitch and enjoy several hours of blessed silence. It's my happy place.
More practically, jury duty is pretty much how LittleBirdy described, except I think that you get $15 for lunch. Then you have to sit through a fairly short video about the importance of serving on a jury and all of the rules. Then you just wait for your number to be called and go to which ever courtroom needs you. When you get to a court room, you have to through voir dire, which is the part where you hear a little bit about the case and then the lawyers ask you questions. Depending on your answers, you might be called up the bench to talk to the judge and the lawyers. Based on your answers, your number, and the size of the jury needed, you are either selected for the jury or dismissed to go back to The Quiet Room.