International constitutional law is like the rules that countries follow when they play together. Just like how you and your friends might have rules when playing games, like not cheating or taking turns, countries also have rules they follow when they interact with each other.
These rules are set out in something called a constitution, which is basically a big list of rules for how the country works. International constitutional law is when lots of countries come together and agree on some of these rules.
For example, they might agree on how countries can trade with each other, or how they can work together to solve problems like climate change. These rules are really important because they help to make sure that countries are fair and respectful to each other.
Think of it like a big game of tag, where everyone agrees on the rules so that no one gets hurt and everyone has fun. International constitutional law is like the rules of that game, but for countries instead of kids.