Moules-frites is a special dish made up of two parts: moules (which is the French word for mussels) and frites (which are French fries). Imagine going to a restaurant and your grown-up friend orders a big bowl full of small, black shells. These are the moules. They are small creatures that live in the ocean and have a tough outer shell to help protect them. They can be cooked in a special way so that the shells open up and you can eat the soft, tasty insides with a fork.
Next to the bowl of moules, you'll see a plate piled high with long, golden sticks. These are the frites! They are made by first slicing up potatoes into long shapes like sticks or fingers, then frying them until they are crispy and crunchy on the outside, but soft and fluffy on the inside.
Now for the best part: when you put both things together! You can use your fork to scoop up some of the moules and dip them in a special sauce if you want. Then you can use your fingers to take some of the frites and dip them into the same sauce or ketchup or mayonnaise or whatever else you like! Moules-frites is a very popular dish in some parts of the world, and people love it because it is delicious, easy to eat and it is popular to share - so you spend a lot of time with your loved ones at the table while eating it!