Mark 9 is a chapter in the Bible. It tells a story about Jesus and his disciples going on a big adventure. On their journey, they meet a lot of people, including a boy who is very sick.
The boy's dad asks Jesus if he can help his son. Jesus says that anything is possible if you believe it can happen. The dad responds by saying that he does believe, but he also has some doubt.
Jesus then helps the boy and he becomes better. The disciples are confused about how Jesus could do this, so they ask him. He explains that it's because they have faith and believe in him.
Later on, Jesus talks to his disciples about how they need to be like children and have pure hearts. He also warns them not to do anything to harm others.
Overall, the story in Mark 9 is about having faith in Jesus and being a good person. It reminds us that anything is possible if we believe in ourselves and have a good heart.