Okay kiddo, so a long time ago, there were some people who believed in something called Christianity. They believed in a man named Jesus, who taught them how to be kind and loving to each other. But not everyone liked this idea and they wanted the Christians to stop believing in Jesus.
So, these Christians who refused to stop believing were punished very badly. They were thrown in jail, hurt or even killed because of their belief! This time when Christians were punished for their beliefs is called the era of the martyrs.
But even though they were being punished, the Christians didn't give up. They stayed strong and continued to believe in Jesus, even if it meant being hurt or killed.
Eventually, the people who were punishing the Christians realized that they couldn't stop them from believing in Jesus. And as time passed, Christianity grew and became more accepted by people around the world.