Okay kiddo, let me explain the Treaty of Tartu to you, which is an important agreement between Russia and Finland.
Imagine, you and your friend have a dispute on something and you want to resolve it by making a deal. That's what happens here between Russia and Finland.
So, long ago in 1920, Russia and Finland had a disagreement about their borders, which means they didn't agree on where one country ended and the other began. They both wanted to have control of a certain area called Karelia.
Let's say that Karelia is like a big piece of pie that both countries wanted to eat. But it's impossible to eat in half, so they needed some help to decide who gets what part of the pie.
That's when a bunch of grown-ups called diplomats came together in tartu (a town in Estonia) to help Russia and Finland reach a compromise. Diplomats are kind of like grown-up friends that help countries solve their problems.
These diplomats made the Treaty of Tartu, which is a document that explained how much of Karelia each country gets to have. It also said that both countries would respect each other's borders and they would be friendly with each other.
So now, Russia had a bigger slice of pie than Finland, but at least they could finally agree on where their borders were. This treaty was supposed to help them avoid any future conflicts and work together more peacefully.
I hope that explanation helps you understand what the Treaty of Tartu is all about.