A border is like a big, invisible line that separates one country from another. In this case, France and the United Kingdom have a border between them. The border is very important because it helps the two countries know where they end and where the other begins.
When people want to travel from one country to another, they usually have to cross the border. This means they have to bring their passport (which is like a special ID that proves who they are and where they are from) and go through a special place called a border checkpoint. At the checkpoint, there are officers who check the passports and make sure that everyone who is crossing the border is allowed to do so.
Sometimes, things at the border can get complicated. For example, maybe there are rules about a certain kind of food or product that can't be brought across the border. In that case, the officers might have to check the things people are carrying to make sure they are following the rules.
Recently, there has been a lot of talk about the France-UK border because of something called Brexit. Brexit is when the UK decided to leave the European Union (EU), which is a group of countries that work together on things like trade and travel. Because of Brexit, there have been some changes to how the border works between France and the UK. For example, there might be new rules about what kinds of things can be brought across the border, or there might be longer wait times at the checkpoint because there are more people who need to be checked.
Overall, the France-UK border is an important place where people and goods cross between two different countries. It helps these countries stay separate but also work together, and it is a reminder that the world is a big and diverse place with many different cultures and languages.