Okay kiddo, so you know how you have a piggy bank where you put all your money in? The government also wants to know how much money people have and where they keep it. That's why there's something called FATCA!
FATCA stands for Foreign Account Tax Compliance Act. It's an agreement between Canada and the United States to share information about people's bank accounts and investments. That means if someone from the US has a bank account or investment in Canada, the Canadian government will tell the US government about it. And if someone from Canada has a bank account or investment in the US, the US government will tell the Canadian government about it too!
The purpose of this agreement is to make sure people are paying their fair share of taxes to their own government. It's important for countries to know how much money their citizens and residents have so they can tax them properly.
So, in simple terms, FATCA is like a big piggy bank for the government to know how much money people have in other countries, so they can tax them properly.