The Passover is a Jewsih holiday and religious festival that is celebrated in April. This is one, if not the, most important of the Jewish religious observances throughout the year. It is there to commemorate all of the trials and tribulations of the Jewish people through the many centuries. The ceremony centres on the deliverance of the Jews from slavery at the hands of the Egyptian Pharaoh. This was done by the work of Moses. Simply leaving Egypt is only part of the story and the best way to celebrate it is via the Passover meal and the special Seder Plates, such as those available from https://cazenovejudaica.com are a minimum requirement.
During the meal it is important to eat the foods laid out on the Seder Plates. Each course represents a feeling and a sensation that the ancient Jews experience or is used to convey it. For example, Parsley is dipped into salt water and eaten to represent the bitter tears that the Jews shed whilst captivity. This is also true of the raw onion and horseradish. The lamb shank is to celebrate the Paschal Lamb that was used to daub the Jewish buildings so that the Angel of Death knew who not to visit.
The meal starts with prayers and then someone, traditionally the youngest person sitting at the table asks why this meal is different from all the others they generally eat. This allows the oldest members to tell the others the youngest what the significance of the meal is.