A treaty of friendship is like a promise between two countries to be nice to each other and work together. It's like when you make a promise to your friend to be kind and share your toys with them.
When two countries sign a treaty of friendship, they agree to help each other and be good friends. They might agree to trade things like toys or food, or they might promise to help each other if something bad happens.
Just like when you make a promise to your friend, both countries have to agree to the treaty and promise to follow it. This way, they can be good friends and work together to make the world a happier place.