FIDIC is like a big rule book that helps people work together to make big buildings or bridges. It has lots of rules for how to make sure everyone is happy and the work gets done right. It's like a game with rules, so everyone knows how to play and what to expect.
The rules in FIDIC are important because they help people get along better and make it easier to build great things. They say things like how to share the work and the money, and how to make sure that everyone is working together to finish the project.
So, it is basically like a big guidebook to help people build big things together while being fair and taking care of each other.