ושחטו אותו כל קהל עדת ישראל בין הערבים
שמות יב ו
Shecht the Korban Pesach
So that we should forever remember the miracles Hashem did for us In Egypt.
On the 14th day of nissan in the afternoon
In the Azarah of the Bais Ha`Mikdash
Klal Yisrael divides themselves into groups and purchases a male lamb or goat that is less than one years old. They then Shecht it in the Azarah on the 14th in the afternoon. They then eat it together after their meal.
Males and females, when the Bais Ha`Mikdash exists.
If you didn't do it
It is punishable by Kareis - this is one of only two positive commandments that have this consequence.
In our times
Since we do not have the Bais Ha`Mikdash, we do not have this Mitzva according to the Chinuch.