Mark 8 is a book in the Bible, which is a big book that tells stories and teachings about God and Jesus.
Mark 8 is a part of the New Testament, which means it talks about the life of Jesus after he was born and grew up. In Mark 8, Jesus does lots of amazing things like healing sick people and feeding a big crowd with just a little bit of food.
One important story in Mark 8 is when Jesus asks his disciples (his closest friends who followed him around all the time) who people say he is. Some people thought he was just a regular guy, while others thought he was a prophet or even the Messiah (which means the chosen one sent by God to save people). But then Jesus asks his friends who they think he is, and one of them named Peter says he believes Jesus is the Messiah.
Another important thing that happens in Mark 8 is that Jesus warns his disciples that he will have to suffer and die, but then rise again from the dead. This is called the resurrection, and it's a really big deal in Christianity (which is the religion that follows Jesus).
So, Mark 8 is a part of the Bible that tells stories about Jesus doing amazing things, and also teaches us important lessons about who Jesus is and what he came to do.