Okay kiddo, the Code européen des voies de la navigation intérieure is a set of rules that govern how boats can safely travel on rivers and canals in Europe.
Just like how you need to follow rules when you play a game or go to school, boats travelling on rivers and canals need to follow rules to make sure everyone is safe.
The Code européen des voies de la navigation intérieure tells boats how fast they can go, where they can and can't travel, and what they need to do to avoid hitting other boats or things like bridges or rocks.
It's important to follow these rules so that people on the boats, people on the land, and the environment around the waterways can be safe and protected.