Seder

The Seder is a way for each participant to relive the Exodus as a personal spiritual event.
The Seder is of a religious nature with a carefully prescribed ritual that makes the dinner quite unlike family dinners held on civil holidays. The ritual is laid out in the haggadah, a book that is followed during the Seder.

The head of the family begins the ceremony by sanctifying the holiday with a benediction (Kiddish) over a cup of wine. In all, four cups of wine (arba' kosot) will be drunk at certain intervals.
After all have washed their hands, the master of the Seder presents celery or another raw vegetable (karpas) dipped in vinegar or salt water to all participants.
Then a shank bone, symbolic of the Paschal lamb eaten in ancient times,
and (commonly) a hard-boiled egg, symbolic of God's loving kindness (or, according to some, a mournful reminder of the destruction of the Temple of Jerusalem), are removed from the Seder plate, while all recite a prayer.

After a second cup of wine is poured, The youngest of the children present asks the four questions (these are in the haggadah) and the adults answer in unison:

The first question: Why does this night differ from all other nights? For on all other nights we eat either leavened or unleavened bread; why on this night only unleavened bread?
The answer: To remind us of the Exodus when our ancestors didn't have the time to bake their bread, and baked it in the hot desert until it was hard. No time to allow the yeast to rise either, so it was flat.

The second question: On all other nights we eat all kinds of herbs; why on this night only bitter herbs?
The answer: To remind us of the bitter, cruel way our ancestors were treated in slavery.

The third question: On all other nights we need not dip our herbs even once; why on this night must we dip them twice?
The answer: We dip our food into Haroset (a mixture of apples, wine and nuts) to remind us of the hard work our forebears did while building the Pharoh's buildings. *The mixture resembles mortar*
And we dip our greens (reminder of spring) into salt water, to remind us of the tears that were shed by the Jewish slaves.

The fourth question: On all other nights we eat either sitting up or reclining; why on this night do we all recline?
The answer: To be comfortable, and to remind us that once we were slaves, and now we are free.