meaning of federalism but make it sound like a 13 year old wrote it and make it simple

Federalism is like when different states in a big country work together to make decisions. Each state has its own rules and power, but they also have to follow some rules made by the whole country. It's like how you and your friends might have your own clubs with your own rules, but when you're all hanging out together, you also have to abide by some basic rules. It's about finding a balance between independence and cooperation.