Okay, kiddo, so you know how Jesus lived a long time ago and was a really important person, right? Well, unfortunately, some people didn't like him very much, and they decided to do something really mean to him. They decided to hurt him a lot, and one way they did that was by making him carry a big wooden cross through the streets, and then nailing him to it. That's called crucifixion, and it's a really painful way to die.
The instrument they used to do this is called a cross, and it's made out of two pieces of wood that are shaped like a plus sign. Jesus was nailed to the cross at the wrists and feet, and he hung there until he died. It was a really sad and terrible thing to happen, but some people believe that Jesus did it to save the world from its sins.
So, the instrument of Jesus' crucifixion is the cross, and it's a symbol of both his suffering and his sacrifice for others. It's now a really important symbol for Christians all around the world, and you might see it in churches or even on jewelry.