In my area, you are notified by mail that you will be in the jury pool during a specific week (5 days). You're assigned a group number and an individual juror number.
Each day of the week they'll announce which group numbers will actually need to report to the courthouse the following morning. If your group doesn't get called in all week then your obligation is satisfied.
If your group number is called then you have to report to the courthouse in the morning. You'll be sent to a waiting room with all the other people called in that day. They'll start calling individual juror numbers at random for assignment to cases. If the end of the day arrives and your number wasn't called then your obligation is satisfied.
If you're assigned to a case then the judge will ask if serving would be a hardship. If so, you can be excused and replaced with another juror from the waiting room. Being excused from duty does not satisfy your obligation, but it does end your jury duty for the week.
That's as far as I've ever gotten.
As for ignoring the summons, that's basically contempt of court. You can be subject to fines and jail time more or less at the discretion of the judge.


I prefer the cows.