Some questions about jury duty?

I just got a summons to appear for Jury duty, and have some questions. It gave me a date to report to the courthouse...so do I just show up that day and if I dont get selected, I dont have to go back again? Also, how do people who are living pay check to pay check and dont have alot of vacation time do it? I think it would be intersting to sit on a jury, but I dont get paid for the time off work and only have a few vacation days left. What if a trial goes on for 2 weeks or more....they just expect you to find a way to live without a paycheck for that long? If I had another means of financial support, I think I would really like to sit in on a jury, but I dont.