A class is the structure of an object, meaning the definition of all items that an object is made up of. An object is therefore the "result" of a class. In reality, an object is an instance of a class, which is why can use interchange the terms object or instance (or even occurrence).
A class is made up of two parts:
If we have a class called car, the objects Peugeot 406 and Renault 18 will be instances of this class. There may also be other objects Peugeot 406, differentiated by their model number. Furthermore: two instances of a class may have the same attributes but may be considered separate distinct objects. In a real world scenario: two T-shirts may be identical, but they are however distinct from each other. However, if we mix them together it is impossible to distinguish one from the other.