So, imagine you're playing a game with a lot of rules, and sometimes those rules don't really work anymore or don't make sense. That's kind of what happened with the Catholic Church a long time ago. They had a lot of rules and things they believed, but some of them didn't really make sense in the modern world.
The Second Vatican Council was a meeting that happened in the 1960s where the leaders of the Catholic Church got together to talk about all the rules and things they believed in. They wanted to make sure that everything they were doing and saying still made sense and was helpful for people.
During the Second Vatican Council, the leaders of the Church decided to make some changes. They decided they wanted the Church to be more open and welcoming to people, to use language that people could understand better, and to be more involved in helping people who were poor or struggling.
Some of the changes the Church made included allowing the Mass to be said in languages other than Latin, making the altar face the congregation, and encouraging people to actively participate in the Mass. They also talked about how important it was to have good relationships with people of other religions, and to work towards peace and justice in the world.
Overall, the Second Vatican Council was a way for the Catholic Church to take a step back and reexamine some of the things they believed in and the way they did things. It helped them make changes that have helped the Church be more welcoming and helpful to people.