you can NOT attend a seder meal
The biblical prohibition against allowing the uncircumcised to eat of the Passover sacrifice applied only to the sacrificial system in the Temple. Since Jews no longer eat sacrificially slaughtered lamb at a Seder, there is no restriction on who they can invite to participate. Note however, that the Seder is a liturgy with a meal as just one part of it, near the middle. The entire liturgy can take several hours, although there are abridged versions.
Seder = סדר
night of passover
No. A Seder is a Jewish religious meal recalling the Passover.
Sometimes.
Four glasses of wine are drunk as part of the seder.
At the Seder meal we retell the story of the Exodus from Egypt.
Generally it occurs only during Passover, a Jewish holiday. There is also a seder for the holiday of Tu Bishvat, but this seder is rarely observed.
One of the foods on the Seder plate is the Z'roa - a roasted shank-bone of lamb or goat, or a chicken wing, or chicken neck. It symbolizes the korban Pesach (Pesach sacrifice), which was a lamb that was offered in the Temple in Jerusalem, then roasted and eaten as part of the meal on Seder night. See also:More abut the Seder meal
At sundown.
It is called a Seder, or "Order" in English
The oldest family member is supposed to read the story of the Exodus during the seder. For the meal part, the oldest man is responsible for reciting certain blessings.
Getting together with loved ones.