We are required to mention the three symbols of Pesach.

The Roasted Shankbone is a reminder for us that we placed lambs blood on the doors of our homes so that G-d would pass over "posach" our homes  when we were slaves in Egypt.  He then killed the first born sons of the Egyptians as the tenth plague.

Matzoh is the flat, unleavened bread which we ate when ran from Egypt in a hurry.  There was no time to wait for the dough to rise.

Moror- Bitter Herbs are to remind us that the Egyptians embittered our lives by making us slaves in Egypt. 

Other symbols are the roasted egg, to remind us of when we would make a sacrifice to the priests at the Temple.  It also serves to remind us that we, the Jewish faith, are strong and adversity makes us even stronger.

The orange at the table is fairly new.  It is a reminder to all that women actually did and do play a part in Judiasm, not just table setting and cooking.