An environmental agreement is like a promise between a group of people (like countries or companies) that they will all work together to help take care of our planet. They agree to follow certain rules and guidelines that will help protect the environment and make sure that things like pollution and waste don't harm the earth too much.
For example, let's say there is a group of five countries that all share a river. The countries might agree to not dump any harmful chemicals or waste into the river, and to work together to keep the water clean for everyone. They might also agree to do things like plant trees, which help clean the air and provide homes for animals.
By making this agreement, the countries are showing that they care about the environment and want to work together to protect it. It's like when you and your friends agree to share your toys nicely and not break them - you're all making a promise to take care of your things and treat each other with respect.