The main function of a bureau-de-change is

A bureau-de-change is a place where people can buy and sell foreign currency. This means that if you are traveling to another country and need the local currency, you can go to a bureau-de-change and exchange your money for the currency of the country you are visiting. Similarly, if you have leftover foreign currency from a previous trip, you can exchange it back for your home currency at a bureau-de-change. In this way, a bureau-de-change helps people to manage their money when traveling abroad.