You eat lettuce dipped in liquid before you eat the meal [this is what we call karpas]. You lay out on the table the matzoh, marror, and charoses in which to dip the marror even though the charoses is not a real mitzvah. You should have two cooked items as a remembrance to the korban pesach and korban chagiga . R’ Eliezer says the charoses is a real mitzvah as a symbolism to the morter in Mitzrayim.

In the times of the Bais hamikdash, they brought the karban Pesach.

Pesachim 10:4

You fill up the second cup with wine. Then a child asks, the four questions. If the child does not know how to ask, the father teaches him the 4 questions.

1. Why on all other nights we eat chametz and matzoh but this night only matzoh?
2. Why on all other nights we eat all greens but this night marror?
3. Why on all other nights we eat cooked and roasted meat but this night only roasted?
4. Why on all other nights we dip once but this night two times.

The father then starts with the disgrace and finishes with the praise and explains from ‘arami oved avi’ until the end.