Okay kiddo, so imagine you're going on a trip to another country. In that country, they probably use a different type of money than what you use at home.
Now let's say you want to buy a cool toy from a store in that foreign country. But the store owner won't accept your money because it's not the same as his country's money.
That's where a foreign exchange office comes in! It's a place where you can take your money from your home country and trade it for the money from the country you're visiting.
First, you go to the foreign exchange office with your money. You'll tell them how much money you have and what money you want to exchange it for. They'll look up the exchange rate - which is how much of the foreign money you can get for your money.
Then they'll give you the foreign money and take your home country's money. You might also have to pay them a small fee for doing the exchange.
Now, when you go to buy that toy, you'll have the right money to pay for it! And that's how a foreign exchange office works - it helps you exchange your money for the money of the country you're visiting.