A croissant is a French pastry made from layers of yeast-risen puff pastry and butter. It is made into the shape of a crescent moon.
A restaurant is a place you go to eat. The chef at the restaurant makes the food for you and serves it to your table. There are many different kinds of restaurants serving many different kinds of food. Some serve cheap food that you can take away, others serve expensive food and fine wines and are a good place to take someone to impress them if you want them to marry you.