Okay, I'll try to explain it to you as if you were five years old. Do you know what Dungeons and Dragons is? It's a game where you pretend to go on adventures with your friends, and you each play as a different character with special abilities.
A cockatrice is one of the creatures that you might encounter on your adventures. It's like a big chicken with wings and a long tail, but it has a special power. If it looks at you with its eyes, you might turn into a statue!
So if you were playing Dungeons and Dragons and you came across a cockatrice, you would need to be careful not to look directly at it. You might try to attack it from a distance with a bow and arrow or magic spells. Or you could try to sneak up on it and attack it with a sword.
But if you do end up getting turned into a statue by a cockatrice, don't worry too much! Your friends can always try to find a way to turn you back to normal. Maybe they'll find a magic potion or a wizard who can cast a spell to reverse the curse.
So that's what a cockatrice is in Dungeons and Dragons - a giant chicken with a dangerous power that you need to be careful around.