Okay, imagine you had a really pretty picture that you drew all by yourself. Now imagine that there are a lot of other people who also drew pretty pictures and they all want to win a prize for their picture.
Well, grown up people do the same thing with movies. They make really good movies in different countries and they want to win a prize for their movie too.
The César Awards are special prizes that grown up people in France give out every year to the best movies made in France and other countries. It's like a big party where they pick winners for different categories, like best actor or best actress.
One of the categories is the César Award for Best Foreign Film. This means that the people in France watched movies from other countries and picked one that they thought was the best. Just like how when you compare your pretty picture to other drawings and decide which one is the best.
So you can think of it like this, the César Award for Best Foreign Film is a really special prize that people in France give to the best movie made in a different country.