Alright kiddo, so you know how we live in Australia and we have a set of rules called the Constitution that help us decide how to run the country? Well, one part of that Constitution is called section 51(i).
Now, section 51(i) is basically a little sentence that says the federal (or national) government has the power to make laws about international trade and commerce. That means they can make rules about buying and selling things between Australia and other countries.
But why is this important? Well, it helps keep our economy strong! See, if the government didn't have this power, it might be harder to trade with other countries because there would be different rules and regulations in each place. But with section 51(i), the government can make sure everyone is following the same set of rules, which makes trading easier and more fair.
So, that's what section 51(i) is all about - it's just a small but important part of our Constitution that helps keep our country's economy healthy.