Okay kiddo, you know when you think something in your mind, like "I want some ice cream," or "I don't want to do my homework?" Mentalism is the belief that the mind, or our thoughts and feelings, are the most important things in the world.
In philosophy, mentalism is the idea that the only things we can be sure of are our own thoughts and experiences. We can't really be certain that anything else exists outside of our mind. So, mentalists believe that our thoughts and experiences are what shape our understanding of the world, and that they should be the main focus of our attention.
For example, if you're playing a game and you're really focused on it, mentalists would say that your experience of playing that game is more important than anything else happening around you. They believe that our subjective experiences are what make life meaningful and that we should try to understand and value them above everything else.
Overall, mentalism is a way of thinking that emphasizes the importance of our own thoughts, feelings, and experiences. It helps us recognize the unique perspective we each have on the world and encourages us to value our own inner lives.