Q: Baruch, David
A: Since you are part of a Messianic Community, don't expect the Seder to be exactly the same as what an Orthodox Seder would be. Presumably you won't be doing the entire service in Hebrew for example. Expect to not eat the main meal until at least an hour or two after the beginning of the Seder. You should have removed the leaven from your house the day before and consumed any remaining food that would have leaven by 10:30 that morning. The rest you should get rid of. This is a picture of sin in your life being driven out. At Pesach we remove the leaven from our house for 7 days. Six months later at Sukkot we remove ourselves from the house for 7 days. Two different pictures of the same thing. There are 4 cups of wine that you drink during the Seder service. The first the the Cup of Santification. Then there is Karpas - dipping of a vegetable into salt water. The salt water is to remind us of the tears that we shed in slavery. (Slavery in Egypt back then, and slavery to sin in our lives.) A package of 3 matzahs is lifed up, the middle one is broken in half and the larger half (yeah, I know, you just can't get these things to break evenly) is wrapped up and hidden. Depending upon your groups tradition, either the children grab it and hide it, or the adults hide it from the children. In either case the adults are expected to ransom it back from the chidlren after the meal is over. The story of the Exodus is retold for all to hear. And the youngest children ask the 4 questions: why are we only eating matzah when other nights we can have regular bread? Why are we eating bitter herbs? What's up with the dipping? Why are we slouching to one side at the table? These questions are then addressed by the adults. 4 sons are described and how they are to be addressed. A wise son, a rebellious son, a simple son, and a son too young to ask. Each is answered in an appropriate way. The 5th son who couldn't be bothered to show up for the Seder isn't mentioned. (But you should still seek him out and pray for his return.) We recount each of the 10 plagues, leaving a drop of wine for each of the plagues. We sing a song called Dayenu. (It would have been enough.) We eat matzah with bitter herbs (horseradish most often). If it is decently strong it should make the top of your head feel like it is about to explode. It is meant to cause you to cry. Feel free to shed some tears. Consider them to be tears of repentance. But this is sweetened with Charoset which is a delicious mixture of apples, nuts and wine. This is a measure of Grace in our times of bitterness. Finally after all of this the Passover meal is served. The Orthodox community will never serve lamb, nor will they serve any roasted meat at the Seder. This is because Torah commands that the Passover lamb only be killed at the Temple. Since there is no Temple, it would be a violation of Torah to serve lamb since it wasn't killed at the Temple as Torah commands. Likewise, Torah specifies that the lamb has to be roasted whole, none of it boiled, none of it fried, etc. Back when there was a Temple they would use pomagranet rods to roast the lambs on since other woods would conduct liquid causing part of the lamb to boil, and likewise metal rods would cause part of the lamb to fry. Since you are going to a Messianic seder they will probably serve lamb. After the meal is completed, the adults have to pay the children to bring back the Afikomen. This is broken and served as the final solid food of the evening. Tradition states that nothing more can be eaten after this so that the flavor of the Afikomen stays with you. The Cup of Redemption is poured, blessed and all drink. Grace after meals is said. The cup of Elijah is poured and a child goes to the door to see if Elijah has arrived to proclaim the coming of Moshaich. The 4th Cup called Hallel is poured. The Hallel is recited (Psalm 113-118). The traditional prayer of Nishmat is recited. This prayer has an interesting history. According to Rabbeinu Tam (Rashi's grandson) this prayer was composed by Shimon Kefa - the Apostle Peter! Everyone says "Next year in Jerusalem" and leaves. Of course this is just a thumbnail sketch of the Seder and it's meanings. For greater detail there are places where you can download a copy of the Haggadah. Check your account's email in-box for example. Most of these will have some level of commentary included as well which will help explain the meaning. Ask others in your congregation what is expected and I am sure they will be glad to help you out. Feel free to ask me if you have any further questions.