Karpas must be eaten because this word contains a hint: if you read it in reverse order, its gematria will be 600 - a clear allusion to the 600 thousand Israelites who were oppressed by hard work.
Karpas must first be dipped in salt water, which reminds us of the bitter tears and suffering of the Jews in Egypt, then the blessing is recited, and then, without saying another word, you have to eat a piece of vegetable.
Baruch Atah Adonai, Eloheinu melech ha’olam, borei p’ri ha’adamah.
Blessed are You, Adonai our God, Ruler of the world, Creator of the fruit of the earth.