The Riga Charter is a plan that people made to help make sure that countries in Europe could work together to keep peace and be friends with each other.
It's like when you have friends over to play and you make some rules so that everyone has fun together and nobody gets hurt. The Riga Charter has rules that countries agreed to follow so that they can work together and not fight.
The rules in the Riga Charter say that countries should talk to each other really nicely and that they need to share information with each other. They also say that countries should help each other out when they need it.
The Riga Charter is like a big agreement or promise that lots of countries made to be good friends and work together.