Imagine you and your friends collect toys and trade them with each other.
All of you live in different neighborhoods and each neighborhood has different rules on how you can trade toys.
Sometimes it's hard to trade toys with friends from different neighborhoods because they have different rules than you.
Now imagine that all the neighborhoods come together and agree on one set of rules for everyone to use.
This would make it much easier to trade toys with friends from other neighborhoods because everyone would be following the same rules.
The Capital Markets Union is like that, but for grown-ups who trade money and investments instead of toys.
It's an agreement between different countries in Europe to make it easier to invest and move money from one country to another.
By having one set of rules for all the countries, it makes it easier for people to invest and businesses to get the funding they need to grow.
This ultimately leads to more money being invested in Europe, which can help create jobs and boost the economy.